A lake formed by debris from a glacier collapse that triggered catastrophic flooding on the China-Nepal border has begun to overflow, the Chinese authorities said on Friday, forcing rescue operations to be halted.

Nepal and China both warned on Thursday of fresh risks of flooding in the Himalayas, with a debris dam creating a lake upstream that had been threatening to collapse.

China had been racing to reduce the risk of more flooding at the disaster-stricken border crossing linking its Tibet region to Nepal, after hundreds were killed in a flash flood on Wednesday.

Risks of the lake bursting and potential secondary disasters such as mountain collapses and avalanches have prompted all Chinese rescue personnel and vehicles to withdraw to stand by in a safe area, state broadcaster CCTV said on Friday.

The lake’s reservoir has topped 2.5 million cubic metres of water, up from the estimated 1.5-2 million cubic metres, a Chinese eight-member engineering team d...