Troops dug burial pits in this quake-shattered town and black smoke poured from crematorium chimneys elsewhere in central China as priorities began shifting Thursday from the hunt for survivors to dealing with the dead. Officials said the final toll could more than double to 50,000.

As the massive military-led recovery operation inched farther into regions cut off by Monday's quake, the government sought to enlist the public's help with an appeal for everything from hammers to cranes and, in a turnabout, began accepting foreign aid missions, the first from regional rival Japan.

Millions of survivors left homeless or too terrified to go indoors faced their fourth night under tarpaulins, tents or nothing at all as workers patched roads and cleared debris to reach more outlying towns in the disaster zone.

Health officials said there have been no outbreaks of disease so far, with workers rushing to inoculate survivors against disease, supply them with drinking water, and find ways to dispose of an overwhelming number of corpses.

"There are still bodies in the hills, and pits are being dug to bury them," said Zhao Xiaoli, a nurse in the ruined town of Hanwang. "There's no way to bring them down. It's too dangerous."

Troops in the town of Luoshui in a quake-ravaged area used a mechanical shovel to dig a pit on a hilltop. Two bodies wrapped in white sheets lay beside it. Down the hill sat four mounds of lime.

In a sign of nervousness, 50 troops lined the road outside Luoshui. Five farmers watched them dig the burial pit, after performing brief funerary rites. Local police detained an Associated Press reporter and photographer who took photos of the scene, holding them in a government compound for 3 1/2 hours before releasing them without explanation.

Across the quake zone in Dujiangyan, troops in face masks collected corpses and loaded them onto a flatbed truck. Thick black smoke streamed from the twin chimneys of the town's crematorium.

Fears about damage to a major dam in the quake zone appeared to ease. The Zipingpu dam had reportedly suffered cracks from the disaster, but there was no repair work or extra security at the dam when it was reached Thursday by an AP photographer, indicating the threat to the structure had likely passed.

People trying to hike into Wenchuan walked on top of the dam as water spilled from an outlet, lowering levels in the reservoir and alleviating pressure on the dam.

Just behind the dam, soldiers set up a staging area preparing speed boats to lower into the reservoir and ferry soldiers in lifejackets, engineers and medical staff up river to Yingxiu, a town flattened by the quake.

The government says "the dam will hold, but then the longer-term question is what to do with it _ to keep it or dismantle it," said Andrew Mertha of Washington University in St. Louis, author of a book on Chinese dams, "China's Water Warriors: Citizen Action and Policy Change,"

The emergency headquarters of the State Council, China's Cabinet, said the confirmed death toll had reached 19,509 _ up more than 4,500 from the day before. The council said deaths could rise to 50,000, state media reported.

The provincial government said more than 12,300 remained buried and another 102,100 were injured in Sichuan, where the quake was centered.

Experts said hope was quickly fading for anyone still caught in the wreckage of homes, schools, offices and factories that collapsed in the magnitude-7.9 quake, the most powerful in three decades in quake-prone China.

"Generally speaking, anyone buried in an earthquake can survive without water and food for three days," said Gu Linsheng, a researcher with Tsinghua University's Emergency Management Research Center. "After that, it's usually a miracle for anyone to survive."

Amazing survival stories did emerge, and were seized on by Chinese media whose blanket coverage has been dominated by images of carnage.

In Dujiangyan, a 22-year-old woman was pulled to safety after more than three days trapped under debris. Covered in dust and peering out through a small opening, she waved and was interviewed by state television as hard-hatted rescuers worked to free her.

"I was confident that you were coming to rescue me. I'm alive. I'm so happy," the unnamed woman said on CCTV.

Premier Wen Jiabao, who has been in the quake zone since Monday as the public face of a usually remote communist leadership, urged those helping the injured to keep up their efforts. Repeating a phrase that has become a government mantra this week, Vice Health Minister Gao Qiang said every effort would be made to find survivors.

"We will never give up hope," Gao told reporters in Beijing. "For every thread of hope, our efforts will increase a hundredfold. We will never give up."

With more than 130,000 soldiers and police mobilized in the relief effort, roads were cleared Thursday to two key areas that took the brunt of the quake, with workers making it to Wenchuan at the epicenter and also through to Beichuan county, the Xinhua News Agency reported. Communication cables were also reconnected to Wenchuan.

Power was restored to most of Sichuan for the first time since the quake, although Beichuan county remained without electricity, Xinhua said.

Much of the official publicity dwelled on efforts to reach the trapped but actual ground operations focused on delivering food and medical aid to survivors and disposing of the dead.

In Dujiangyan, on the road between the provincial capital of Chengdu and the epicenter, a dozen bodies lay on a sidewalk as police and militia pulverized rubble with cranes and back hoes. The bodies were later lifted onto a flatbed truck, joining some half-dozen corpses.

At the crematorium, some grieving relatives were rushed through funeral rites by harried workers. Scores of bodies lay on concrete in a waiting area _ outnumbering the handful of chapels usually used in funerals.

Thick black smoke streamed from the crematorium's pair of chimneys as families cleaned and dressed the dead in funeral clothes, including fresh socks and sneakers for children.

Fireworks were set off every few minutes and families burned incense, candles and spirit money. Such traditions meant to send the dead peacefully into the afterlife were once banned by the communist authorities but have revived in recent years with free-market reforms and rising prosperity. Burial, which likewise the government once tried to stamp out, has become common in the countryside, although still difficult for people in crowded cities.

In an appeal posted on its Web site, the Ministry of Information Industry called on the Chinese to donate rescue equipment including hammers, shovels, demolition tools and rubber boats _ 100 cranes were also needed, it said.

The International Federation of Red Cross and Red Crescent Societies has also issued an emergency appeal for medical help, food, water and tents.

After initially refusing offers of foreign aid workers, China welcomed a Japanese rescue team. Made up of firefighters, police, coast guard and aid officials, the first half of the team arrived in Beijing on Thursday and would head to the disaster area Friday, Xinhua said.

Japan and China have been at odds for years over disputed borders, Japan's treatment of its wartime invasion of China, anti-Japanese protests in China, and general Japanese unease over Beijing's rapidly growing diplomatic, military and economic power. Leaders of the two countries met in Tokyo earlier this month to try to resolve their differences.

The Foreign Ministry said Russian, South Korean and Singaporean teams would join soon.

China had so far received international aid worth more than $100 million and materials worth more than $10 million, Foreign Ministry spokesman Qin Gang said at a briefing. But it still needed supplies of tents, clothes, communication equipment, machines for disaster relief, and medicines, he said.

"The Chinese authorities have done a fantastic job mobilizing troops, but troops are not everything. You need specialist teams with equipment otherwise you're not going to find them," said John Holland, operations director of Rapid UK, a search and rescue charity with two decades of experience handling international disasters.

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Associated Press writers Audra Ang in Mianyang, Christopher Bodeen in Dujiangyan, and Cara Anna and Anita Chang in Beijing contributed to this report.