Soldiers had worked for days to defuse the Tangjiashan "quake lake," now with a volume of more than 80,000 Olympic-size swimming pools, but according to the China News Service, multiple threats still loomed.
Liu Ning, chief engineer at the Ministry of Water Resources, warned at a briefing late Tuesday that one of the risks was aftershocks, which could breach the lake any time, inundating lower-lying areas.
"The area still receives constant aftershocks, and especially aftershocks of over six on the Richter scale could have an impact," said Liu, according to the news service.
"After several measures undertaken at the lake, the situation remains extremely dangerous," the news service said, citing Liu.
The lake was created when the May 12 magnitude-8.0 earthquake rattled southwest China's Sichuan province, triggering a massive landslide that blocked a river cutting through the mountainous area.
Since then, officials have been watching anxiously as the lake has built up, warning it could endanger more than a million people if it were to break through the barrier.
Last week hundreds of soldiers dug a channel, hoping it would help drain the lake, and at least contain it, once it reached a certain level.
As of late Tuesday, the surface of the lake was edging closer to the top of the dam, reaching just 2.37 metres (eight feet) below the lowest point of the blockage, according to the China Daily website.
It remained to be seen whether the water could be directed successfully into the newly dug channel, according to the paper.
The Sichuan government has earmarked 200 million yuan (29 million dollars) to spend on controlling the three dozen swelling lakes that threaten to burst and flood the downstream regions, the paper said.
The death toll from China's earthquake rose on Tuesday to 69,107, with another 18,230 missing, the government said. The new toll, given by the state-run Xinhua news agency, marked an increase of 88 from the day before.
Another 373,577 people sustained injuries in the May 12 quake, China's worst natural disaster in a generation.
Soldiers were still scaling mountains and hacking their way through thorny undergrowth in a desperate attempt to find a downed military transport helicopter, Xinhua news agency said.
President Hu Jintao, also the nation's commander-in-chief, instructed the rescuers to spare no efforts to locate the helicopter, even as landslides made the effort even more difficult.
As of late Tuesday, more than 10,000 troops had been unable to come across even a trace of the army Mi-171 chopper or the five crew members and 14 injured quake survivors aboard, Xinhua said.
It added the search for the helicopter, which crashed in heavy fog four days ago, would continue by daybreak on Wednesday.
Meanwhile, the government also took steps apparently aimed at countering rising anger over the deaths of thousands of schoolchildren in school collapses.
Police and soldiers on Tuesday blocked access by residents and journalists to the ruins of the Juyuan Middle School near the city of Dujiangyan, where hundreds of students were believed to have been buried.
"The scene is no longer open. We cannot say why. Please understand," a police officer there told AFP.
Residents said police told them the restriction was aimed at "protecting" the site, where distraught parents had come regularly to mourn their children.