An earthquake-formed lake swelled Monday despite soldiers' efforts to speed its drainage by blasting boulders in a diversion channel with dynamite and anti-tank weapons.

Authorities remained on alert after yet another aftershock jarred the Tangjiashan lake, which could flood more than 1.3 million people downstream if the water flow is not controlled.

Managing the lake, formed when a landslide set off by the powerful May 12 earthquake blocked the flow of the Tongkou River, was the latest challenge for the Chinese government.

Beijing was already shouldering the burden of caring for the 5 million people left homeless by the disaster, which killed nearly 70,000.

Military engineers fired ammunition at massive rocks in a spillway dug to relieve pressure on the unstable barrier blocking the river, the official Xinhua News Agency reported. Soldiers have also used three tons of dynamite over the past two days to blow up boulders and double the width of the channel to 33 feet (10 meters), the report said.

The flow in the channel increased after more than 10 explosions, but it was still not keeping up with the water gushing into the lake from the blocked river behind the dam.

On Monday, about 120 Chinese People's Liberation Army troops were sent to reinforce the operation at the lake, where crews were deepening the diversion channel and digging a second spillway, Xinhua said.

The water level was more than 6 feet (2 meters) above the mouth of the spillway and rising, Xinhua said. Authorities were on alert for threats to the dam's stability including increased rainfall, new aftershocks and landslides that could deposit rubble in the lake and push water levels even higher.

A magnitude 5 aftershock rattled parts of the disaster zone, including the Tangjiashan lake, Monday afternoon. Rocks rolled down mountainsides and the dam shook, Xinhua reported. It later said the situation was stable.

The 10-second aftershock sent people in the hard-hit county of Wenchuan rushing out of shaking buildings and tents, Xinhua said. There were no reports of damage or casualties.

David Petley, a geography professor at Britain's University of Durham, said news photos showed worrisome signs including indications that the top of the Tangjiashan dam was holding, instead of eroding slowly as it should, while the channel further down was eroding too quickly.

That could put increased pressure on the dam by suddenly sucking down large volumes of water, Petley said.

Meanwhile, 15 government officials in Sichuan province, where the May 12 quake was centered, have been removed from their posts for slow responses or wrongdoing during relief work, Xinhua said. Another 13 were punished for wrongdoing during quake relief, the report said, without elaborating.

The death toll from last month's magnitude 7.9 quake climbed Monday to 69,142, with 17,551 people still missing.

More than 250,000 people downstream from Tangjiashan lake have been evacuated in recent weeks. Many were living in improvised camps on surrounding hillsides, surviving on instant noodles and suffering from heat, mosquitoes, and a lack of water for bathing.

Lu Raoxuang, a farmer in Hongye village about 28 miles (45 kilometers) downstream from Tangjiashan, said authorities forced him up a nearby hillside one day late last month when he returned home from tending to his crops. He said he was not even allowed to wash his face before evacuating his two-story brick and concrete home, which was badly damaged in the quake.

The villagers in Lu's camp were free to move about during the day, and he has regularly returned to check on his home. But the wiry 58-year-old farmer said he was not allowed to tend to his crops, leaving his corn and sweet potatoes neglected in the field.

"Our land is down here. I don't want to leave my land," Lu said. "I just have to wait for the water and see if it really floods. I'm really worried. I don't know what my future is."