CHENGDU, China—Rebuilding China’s devastated earthquake zone will be a long and arduous process, the government warned Wednesday in a signal to millions of survivors living in tents that there will be no quick return to normalcy from their upturned lives.

Infrastructure problems—from rehousing entire townships destroyed by the quake to digging channels to divert blocked rivers—are among the most pressing for officials more than two weeks after the disaster.

In addition to trying to house some 5 million people left homeless by the May 12 quake, officials say hard-hit Sichuan province is still prone to landslides and the conditions are hampering recovery and reconstruction efforts.

“We are racing against time to repair damaged infrastructure,” Mu Hong, a deputy director at the National Development and Reform Commission, the country’s top economic planning body, told reporters Wednesday. “Due to the immense magnitude of loss resulted from the quake, production recovery and reconstruction of the quake-hit region will be arduous in the near future.”

The slow progress of reconstruction and the continuing threat of new disasters meant some were preparing for a long stay in temporary housing.

“When we are able to go back to our home village we will still have to live in this kind of tent for some time,” said Wu Shida, whose village of Huangshi was emptied by soldiers this week because of the flood threat.

The villagers are now living in a camp near Jiangyou town. “I don’t know how long but best hope will be till the end of this year,” Wu said.

The magnitude 7.9 quake sent dirt and rocks tumbling into valleys, blocking roads and clogging rivers that have developed into fast-rising lakes behind the impromptu dams.

Some 158,000 people have been evacuated from downstream of the largest of the quake-spawned lakes, which officials are rushing to drain before it breaks through a wall of debris and floods the valley below.

At the newly formed Tangjiashan lake, about 2 miles upstream from the devastated town of Beichuan, hundreds of soldiers labored for a third day building channels to divert the fast-rising waters.

Yang Hailiang, the official heading the Tangjiashan operation, said teams working around the clock had completed a third of the work needed to drain the lake, the official Xinhua News Agency said.

There are no roads leading to the site, and helicopters flew in 40 earth-moving machines to do the digging, Xinhua said. The soldiers have also used explosives to destroy debris blocking the digging, state media said.

Officials have said they expect rebuilding the quake zone will take at least three years.

The number of confirmed deaths from the earthquake climbed toward an expected toll of more than 80,000 Wednesday, with China’s Cabinet saying 68,109 people were killed and 19,851 were still missing.

The entrance to Beichuan, which was largely abandoned after the quake, was blocked by soldiers Wednesday. A sign erected on the quake-buckled road leading into town said: “Completely restricted area. Absolutely no entry.”