The fight to drain a dangerous debris-formed lake gained new urgency Wednesday amid fears that a breach could bring further devastation to a northwest China county that was leveled by the country's deadliest mudslide in decades on Sunday.

The weather bureau warned Wednesday of heavy rains and more potential geological disasters in the next five days on the upper reaches of the Bailong River, above Zhouqu County, in Gannan Tibetan Autonomous Prefecture of Gansu Province.

The rains could cause the unstable lake on the Bailong River to burst and flood the already-devastated areas where people are still hunting for survivors.

The provincial government has ordered a mass evacuation of residents in areas prone to flooding and geological disasters.

By 8 a.m., the water level of the lake was down by 80 cm from the highest level reported after the mudslide swept through the county on Sunday, the emergency rescue headquarters said in a press release.

Meanwhile, it said, the lake's water volume had been halved from 1.5 million cubic meters to 700,000 cubic meters.

The unstable lake was created by debris that blocked the Bailong River.

Troops have been using excavators and explosives to demolish the blockage and discharge potential flood waters since Monday.

The mudslide, which happened in the early hours on Sunday, has killed at least 702 people and left 1,042 others missing in Zhouqu County.

The hunt for survivors entered its fourth day Wednesday, with troops still searching the ruins with life detectors and sniffer dogs.

Hopes are fading after the end of the 72-hour "golden window" for survivors, considered the optimum time for rescue. Grieving residents are seen wailing in the debris, still hoping to retrieve at least the bodies of their loved ones.

Eight excavators are expected to arrive in the county seat Wednesday, after roads were repaired to give access to relief vehicles the previous day.

When the heavy machines start leveling the debris, the residents' last hope of giving the deceased a decent burial will be gone.

Many rescuers are also caught in a dilemma of how to handle the bodies. Immediate cremation would be ideal for epidemic prevention, but in Zhouqu County, where at least a third of the residents are Tibetans, traditional burial is still one of the most prevalent funeral customs.

"We encourage people to cremate the bodies of their deceased family members as soon as possible, but many people want to keep the old custom of burial," said Yang Yuqiong, a doctor at a local clinic.

Yang and her colleagues are worried about disease in the devastated area, which is hit alternately by blazing heat and rain.

With roads to the devastated areas reopening to relief vehicles Tuesday, more supplies were trucked in.

"Now at last, tents, food and clothing have arrived to ensure everyone is fed and sheltered," said Ma Chengxiang, an official with the rescue headquarters.

The psychological trauma, however, would take much longer to heal.

Ma said most survivors were staying with friends and relatives away from home, except those who still hoped to be close to their missing, or deceased family.