Most of the deaths occurred in the central tea-growing district of Badulla, where 16 people were buried alive when mountain slopes crashed onto their homes overnight, the Disaster Management Centre (DMC) said in a statement.

Another four were killed in a similar manner in the adjoining Nuwara Eliya district. The remaining fatalities were reported elsewhere.

Nearly 400 homes were damaged in mudslides, with over 1,100 families moved to temporary shelters.

The DMC said river levels were rising across Sri Lanka and warned residents in low-lying areas to move to higher ground.

Sri Lanka is currently experiencing the northeast monsoon season, but rains have intensified due to a depression east of the island, it added.

The government suspended final year school examinations nationwide for two days because of the weather.

More than 100 millimetres of rainfall was expected across Sri Lanka, with some areas in the northeast forecast to be deluged with 250 millimetres of rain on Thursday.

This week's weather-related toll is the highest since June last year, when 26 people were killed following heavy rains. In December, 17 people were killed by flooding and landslides.

Sri Lanka depends on seasonal monsoon rain for irrigation and hydroelectricity, but experts have warned that the country faces more frequent floods due to climate change.