A military helicopter carrying 19 people, many of them injured in China's devastating earthquake, crashed in fog and turbulence, and authorities were searching for survivors, state media reported Sunday.

The Russian-designed Mi-171 transport helicopter crashed Saturday afternoon in Wenchuan county in China's quake-hit southwest, the official Xinhua News Agency reported. Xinhua said late Sunday that the aircraft was carrying 5 crew and 14 others, including people with quake injuries.

There was no immediate word on any survivors or casualties. Xinhua said a search-and-rescue operation was under way.

Meanwhile, troops equipped with diggers and backhoes finished digging a channel to siphon off water from an earthquake-formed lake that authorities feared could burst and further devastate stricken areas.

The lake formed above Beichuan town in Sichuan province when a hillside plunged into a river valley during the May 12 quake. It is the largest of more than 30 quake-formed lakes.

More than 600 troops who had been working around the clock for six days finished digging the trench Saturday evening, Xinhua said. The channel — nearly 500 yards (meters) long and up to 10 yards (meters) wide — was meant to drain off some of the lake as its water level continues to rise, Xinhua said.

As a precaution, authorities were also evacuating about 200,000 people who could suffer from flooding if the lake bursts.

Downstream, people packed belongings and evacuated the villages of Jiuling and Qinglian on Sunday. Soldiers in camouflage fatigues and orange life vests patrolled the empty streets. Warnings spray-painted in red on one building in Qinglian showed how high waters might reach if the dam bursts.

The confirmed death toll from China's worst quake in three decades stood at more than 69,000, with nearly 19,000 others still missing.

Two men who had been stranded in Sichuan's mountains with injuries from the quake were airlifted out Sunday by a Hong Kong-provided helicopter, Xinhua said. Six soldiers who parachuted in found the men, both miners, a day earlier and treated them.

The quake was especially painful to many Chinese because it killed so many children — many of whom had no siblings because of the government's population-control policy that limits many families to one child. Citing Sichuan's head of family planning, Xinhua on Saturday reported that an estimated 7,000 children without siblings died and another 16,000 were injured.

The destruction of almost 7,000 classrooms has led to complaints from angry parents that schools were poorly built.

In the town of Juyuan, about 100 parents marked International Children's Day on Sunday by gathering to mourn their children killed when a middle school collapsed. The parents also vented their anger at school and local officials.

On a large, white banner hanging on a part of the school that still stands, someone had written that "a blood debt" should be paid by those responsible for allegedly shoddy construction.

One parent circulated a letter that thanked the Communist Party and government for their help but also said parents were suing school leaders and local education authorities.

To reporters taking photos, one parent yelled, "The next time you go to a news conference, ask a lot of questions. Help us get justice for our dead babies!"

China's Cabinet has ordered appraisals of all school buildings in the quake zone, according to Xinhua. It quoted a Construction Ministry investigator, Chen Baosheng, as saying that reinforcement rods in the Juyuan Middle School — where 900 students were buried — "were too thin."

Chen Huaqun said her 15-year-old son died in the school.

"They dug out three bodies yesterday and there are still six more in there," she said. "The parents asked them to keep digging a few days ago, but officials told us they won't be able to find anymore bodies. But yesterday, they found three. How could the officials be so cruel?"