A woman cries as the body of her husband is found under the rubble of a collapsed apartment house in Mianyang, in China's Sichuan Province. Three days after a massive earthquake hit the area, China warned Thursday that the death toll could soar to 50,000.

Luoshui Town, China ? 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.

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.

Dam concerns ease

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.

Survival hopes fade

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 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.”