CHENGDU, China -- A stockpile of chemicals being used to disinfect an earthquake-shattered Chinese town ignited Thursday and injured scores of soldiers doing relief work, adding to a day of problems for urgent recovery efforts.
Heavy rain also added to the misery of crowds of homeless survivors living in tents or lean-tos and hampered troops rushing to drain a quake-spawned lake before it floods a valley filled with villages.
The chemical fire took place in the town of Leigu, in devastated Beichuan county. The official Xinhua News Agency reported that more than 800 people were evacuated to avoid a cloud of dense chlorine gas caused by the blaze.
As in many destroyed towns, officials have been spraying disinfecting bleach on streets and rubble in an effort to prevent disease breakouts. Thousands of people are still missing and their bodies could be buried in the rubble, while rats and other scavengers have been reported in some places.
But one expert said the spraying of bleach on rubble has little effect except perhaps a psychological one for victims.
"It really doesn't make much sense because it's not doing much good," said Claude de Ville de Goyet, the retired emergency preparedness director for the Pan American Health Organization and a consultant who works disaster sites. "It's cosmetic."
He said that even if there were a cholera outbreak -- which there is not -- spraying the surface of rubble would not help. Bleach does work well to disinfect water.
State-run television showed smoke billowing over Leigu and reported that a stockpile of bleach powder had ignited in a storage building. CCTV footage showed soldiers spraying down the building and extinguishing the threat, and then several soldiers who were gasping for air being treated by medics.
"The soldiers have inhaled the fumes, it has affected their bodies, and they are in the military hospital now," said a soldier, identified by CCTV as the leader of the fire crew. His name was not given. He said 61 soldiers were injured. Xinhua reported that four people were injured. It was not immediately possible to reconcile the different injury tolls.
It was not immediately clear why the bleach ignited, though substances in it can turn explosive if heated or mixed with hydrocarbons such as those in diesel fuel.
Rain, meanwhile, grounded helicopters helping in operations to drain the Tangjiashan lake, which formed above Beichuan town after a quake-triggered landslide blocked a river.
With roads to the area cut off, helicopters have airlifted 40 heavy earth-moving machines to dig drainage channels. Heavy rain prevented aircraft from flying Thursday, CCTV reported, though workers were able to continue clearing debris. The rain added marginally to the rising waters, but was a minor factor compared to the river feeding into the lake.
In three days of around-the-clock work, troops have dug a 50-yard-wide channel running 300 yards long, CCTV said, without saying how much further work was needed.
The government Thursday raised the confirmed death toll from the quake to 68,516, with 19,350 people still missing. The government has said it expects the final tally to surpass 80,000.
The rain made conditions worse for the 5 million people left homeless by the quake, increasing the threat of more landslides.
"Before the earthquake the mountains here were completely covered with trees and it was green everywhere. You could not see any naked rock in the mountains," said Zhou Liqiong, resident of Hanwang town. "Now the continuous landslides have changed the look of the place. You can see the naked mountains everywhere."
Some 158,000 people downstream from Tangjiashan lake have been evacuated, and officials have pledged to warn other nearby residents in case of flooding so they have time to flee. Troops have sealed off Beichuan to the public.
Of 34 lakes created by the earthquake, 28 are at risk of bursting, Xinhua said.
The military released some details of the massive recovery effort. Lu Dengming, commander for the area around Chengdu, the capital of hardest-hit Sichuan province, said more than 2,500 miles of damaged roads have been repaired and 70 million cubic feet of ruins cleared, the official Xinhua News Agency reported.
Some 178,000 troops, militia and reservists were taking part in the operation, and had delivered more than 510,000 tons of relief materials by land and air, including tents and prefabricated houses and schools, Lu said.
Foreign Ministry spokesman Qin Gang said Beijing was in talks with Tokyo about the sensitive issue of using the Japanese military to deliver earthquake relief, in what would be the first significant military dispatch involving the two countries since World War II. No decision was made Thursday.
Japan invaded China and conquered large parts of it in the 1930s before being defeated by the Allies in 1945, and many Chinese still strongly resent Japan for its military aggression.
Japanese media reported Friday that the government had decided against using it military for the mission.
South Korean President Lee Myung-bak, who is visiting China, will travel to the disaster region Friday, Qin said.
Also Thursday, the head of the world's most famous panda reserve, badly damaged by the earthquake, said it was looking for a new home.
"What I'm worrying about are secondary disasters, such as severe aftershocks," Zhang Hemin, chief of the Wolong Giant Panda Reserve, said by phone. "The road is easily blocked by rocks falling from the mountain. There would be no way to get the food in."
One panda remains missing. Conditions remain so bad that the government last week arranged an emergency food shipment of about 5 tons of bamboo for the 47 pandas still at the reserve. Some pandas have been moved to another breeding center in Chengdu, and eight were flown to Beijing last weekend for a previously scheduled stay for the Olympics.
Associated Press writer Seth Borenstein contributed to this report from Washington.