©Getty images

A rescue team attends to a quake victim at the Zipingpu Dam Wednesday.

China's state TV has said that the death toll from this week's massive earthquake could reach 50,000, news agencies have reported. The official death toll in southwestern China has now topped 19,500, Sichuan provincial government officials said Thursday, according to state-run media.

But casualty figures from various cities indicate a higher number of dead. The state-run Xinhua news agency has provided death tolls for eight communities in Sichuan province alone that add up to nearly 20,000, including roughly 7,700 who perished in the town of Yingxiu, near the earthquake's epicenter.

CNN cannot independently confirm the tallies.

More than 4.3 million homes have now collapsed or sustained damage from the 7.9 magnitude quake, according to the Chinese Embassy in Washington.

Authorities say nearly 400 dams were damaged by this week's massive earthquake, according to The Associated Press.

Two thousand troops have already been sent to the Zipingpu Dam, near Dujiangyan City, after state-run media said that it had "severe cracks. A probe later revealed that the dam is stable and safe, state news agency Xinhua reported.

The waters at Zipingpu are now being lowered to decrease pressure on the structure, according to business news magazine Caijing, AP reported.

The agency also reported the economic planning agency as stating that almost 400 mostly small dams had been affected by the 7.9-magnitude quake, while the Ministry of Water Resources has ordered a check on reservoir facilities throughout the nation.

International Rivers, a U.S.-based group which says it opposes "destructive dams and the development model they advance," alleges on its Web site that experts at China's Earthquake Bureau warned eight years ago that Zipingpu dam was at risk due to its closeness to significant geographic faultline. The Chinese authorities have not responded to the comments.

Chinese Prime Minister Wen Jiabao Thursday ordered 90 more helicopters for rescue missions in Sichuan province, as mudslides, debris and fallen rocks blocked rescuers and aid workers from reaching quake-hit areas, Xinhua reported. Thursday's order brings the total to 110.

China's Foreign Ministry has allowed Japan to send a professional rescue team to the earthquake zone, the Xinhua Web site said. Japan -- which has had strained relations with Beijing in recent years -- has extensive earthquake-rescue expertise, suffering many large tremors throughout its history.

The Red Cross for the island of Taiwan, which China has been in dispute with since 1949 and which it regards as a renegade province, said it is being allowed to send a 20-man team, AP reported.

Saudi Arabia, the United Kingdom, Germany, Vietnam and Poland are among the countries providing assistance, according to Xinhua.

Meanwhile rescuers have continued their attempts to save those trapped beneath the rubble at schools, businesses and homes.

In Beichuan, parents of middle-school students waited, hoping recovery teams would pull their children alive from the rubble of a middle school. But they found little hope in their exhausting three-day vigil as search teams pulled out one lifeless body after another.

A few roads to Wenchuan county -- the epicenter of the quake -- started to open, allowing military trucks to begin their haul to affected sites, while rescuers continued their attempts to save those trapped beneath the rubble at schools, businesses and homes.

Shortages of water are making an already difficult situation worse. State media reported a lack of drinking water in the town of Yingxiu in Wenchuan, saying many people have not had any water since Wednesday.

Aftershocks at times forced rescuers to turn away from the fallen buildings, leaving crowds frustrated without knowing the fate of loved ones. Video from one disaster scene shows a woman clinging to a crane after rescuers suspended a mission at a crumbled building, deeming the site to dangerous to enter.

But there were scattered stories of survival. A three-year-old girl was rescued from beneath a toppled building in Sichuan's Beichuan County on Thursday, Xinhua said. Photos of the rescue showed the girl sustained a leg injury, but was otherwise alert.

A frightened seventh-grade girl was pulled safely from the rubble of a school dormitory Wednesday evening -- 50 hours after she was buried by Monday's earthquake, state-run media said.

In a weak voice, the trapped girl called out to one of the rescuers, "uncle, save me, save me," he said. "If anything (bad) had happened to her, the voice could haunt me for the rest of my life."

The girl rescued at Muyu Middle School in Sichuan province was among 89 children pulled from the rubble alive. At least 201 students were killed when the building collapsed while many were napping, according to China.org. More than 100 children escaped from the school in Qingchuan County, and rescuers were searching for an unspecified number still believed to be trapped.

Wang Guangfen, a nurse, climbed under a cement slab to give the girl, He Cuiqing, medicine, while other rescuers carefully moved slabs until they could remove the girl.

"She appeared very fragile, and there were blood stains on her chest," said China.org, quoting Wang. "But she was still conscious, and called me aunt when I reached her."

Elsewhere in the stricken region, videotape showed a three-year-old pulled out alive after more than 40 hours in rubble, and a pregnant woman safely rescued, as a small crowd cheered.

Those who escaped injury stand in long lines for hours to register the names of the thousands missing family members with government officials. One woman at a makeshift refugee camp in Mienyang, about 40 miles outside Beichuan, told CNN she hasn't heard from her husband or parents: "I hope to find their bodies, I'm sure they're dead."

Along Sichuan roads, piles of supplies, especially blankets and clothes, sprung up. In Mienyang, there was enough in one pile to distribute to the 10,000 people camping out at the nearby stadium. Others swarmed trucks delivering food and water.

In other developments:

# Video showed soldiers and relief teams swarmed over mountainsides and piles of debris in and near the epicenter of the quake in Sichuan province, looking for signs of life. Helicopters were flying overhead, some of them dropping food and other supplies.

# Twelve American eco-tourists who were thought to be missing Monday after the quake were able to contact their loved ones by cell phone to let them know they are alive, said an official with World Wildlife Fund, which sponsored the tour. But two Chinese WWF volunteers remain missing.

# Fifteen British nationals have been reported missing near the panda preserve. "We have no reports so far of any casualties to British citizens, but we do remain very concerned about reports of some UK citizens being in the affected area," said William Ehrman, British ambassador to China. "We are doing everything that we can to locate them."

# More than 30,000 people are "missing or out of reach" in Shifang, Xinhua reported. Citing local government, Xinhua said that the death toll in the city exceeded 2,500. Two chemical plants collapsed, trapping hundreds of people, Xinhua reported Monday. More than 80 tons of of ammonia leaked out, it said. A local official said there were no deaths. The news agency's Wednesday report made no mention of the people it had said were trapped in the chemical plants.

# Mianyang has become a massive refugee camp for survivors, Xinhua reported. Thousands of people uprooted around the region are taking shelter downtown at the city's main sports gym and other facilities. Reports say 7,395 people have died and 18,645 are trapped in debris in the city. Among those trapped were about 1,000 students at a middle school.