The death toll from the catastrophic floods that struck Nepal and China's Tibet this week has risen to 750, while more than 3,000 people remain missing, as authorities warned of possible fresh flooding and rescuers continued operations in difficult conditions.

Nepal's disaster agency said that 823 people remained out of contact on Thursday, more than 24 hours after a deadly flood tore through the border region with Tibet.

The death toll from devastating flash floods and landslides along the Nepal-Tibet border has risen to at least 362.