Ninety-one people have been killed and 110 others are missing amid flooding and torrents of mud unleashed by heavy rains in Sri Lanka.

Authorities have appealed for international help to assist rescue and relief operations.

The Disaster Management Centre said tens of thousands of people have been displaced by the rain which started early on Friday.

The foreign ministry has appealed for assistance from the United Nations and from other countries.

The government advised people living near swollen rivers and hilly slopes prone to landslides to evacuate, as heavy rains are expected to continue.

Navy boats and air force helicopters were deployed to rescue marooned victims and provide emergency relief.