MIANYANG, China — Chinese authorities had evacuated nearly 200,000 people by early Saturday and warned more than 1 million others to be ready to leave quickly as a lake formed by a devastating earthquake threatened to breach its dam.

The confirmed death toll from China's worst quake in three decades was raised Saturday to 68,977, an increase of about 120 people from a day earlier. Another 17,974 people were still missing, the State Council said. The increase was the smallest since the government started issuing a daily death toll shortly after the quake hit on May 12.

Hundreds of Chinese troops have been working around the clock to drain Tangjiashan lake in Sichuan province. The lake formed above Beichuan town in the Mianyang region when a hillside plunged into a river valley during the quake.

The official Xinhua News Agency said work on a runoff channel had been completed. It quoted Yue Xi, deputy chief of the water and electricity section of the People's Armed Police, as saying water was expected to be discharged between Sunday and Tuesday.

Xinhua said 197,477 people were evacuated to safe ground by Saturday morning. It did not say how the exact number was arrived at, and many of the people may have moved just short distances to higher areas.

The news agency said Tan Li, the Communist Party chief of Mianyang, had issued another order calling for all 1.3 million people in the area to be evacuated if "the barrier of the quake lake fully opens" and floods the area.

An official with the press office of Mianyang City Quake Control and Relief Headquarters, who would give only her surname of Chen, said Saturday's drill would involve testing the command system of various levels of government officials to ensure that any order to evacuate — if it comes — would be passed on quickly to everyone in the valley.

No public broadcast of the evacuation order would take place.

There was no sign that the dam was about to burst. Troops have sealed off Beichuan to the public.

Tangjiashan is the largest of more than 30 lakes that have formed behind landslides caused by the quake, which also weakened man-made dams in the mountainous parts of the disaster zone.

Millions of people in Sichuan are already living in tent camps and prefabricated housing, which have taken on the tone of new villages.

In Mianyang, about 200 families left their camps in flood-prone areas of the city and moved to higher ground in a wooded park on Fule Mountain. Most had camping tents and shelters made of tarp pitched under trees amid ornate gazebos and tea houses with tradition sloping yellow tiled roofs. Red signs on the buildings said, "Dangerous building, don't come near."

One woman, who only gave her surname, Wang, said life was uncomfortable but fine under the circumstances. "We've got all the basics. Those who are out of work are being given food, but my company is taking care of me," said Wang, who was living in a camouflaged camping tent set above the ground on wood planks.