Flood warning notices were sent to people’s phones early Sunday as rescue crews worked to clear a major highway connecting Kathmandu to one of the areas worst hit by Wednesday’s catastrophic floods, which killed at least 800 people and left more than 3,000 missing in Nepal and Tibet.

The latest warnings came after Chinese authorities informed their Nepalese counterparts of increased water flow upstream, according to Dharam Raj Uprety, chief executive of Nepal’s National Disaster Risk Reduction and Management Authority.

The Chinese state news agency Xinhua, citing the country’s water resources ministry, said a new lake formed after Wednesday’s floods high in the mountains had largely drained.

But Xinhua said the ministry warned that a crater located 5.6 kilometers (3.5 miles) upstream, which held an estimated 1.4 million cubic meters (370 million gallons) of water, still posed some risk and required close monitoring.

Nepal’s disaster agency said Sunday the death toll had climbed to 788 with 2,502 missing, while Chinese authorities reported 16 deaths and 546 missing on the Chinese side of the border.