Nine people are dead and two others missing after floods in Sri Lanka and parts of southern India caused by more than a week of pounding rains.

Nearly half of Sri Lanka's 25 districts have been hit by the deluge, with the worst affected areas in and around the island's tea-growing Central Highlands.

"Five deaths and two disappearances were reported" across Sri Lanka since the rains began at the end of October, Pradeep Kodippili of the island's disaster management agency told AFP on Monday.

More floods are likely in the coming days with downpours set to move to the country's northern coast around the city of Jaffna, the country's weather bureau warned.

Four people have also died in "rain-related incidents" across India's Tamil Nadu state, local disaster management minister K.K.S.S.R. Ramachandran said on Sunday.

Authorities had established more than 150 relief camps to distribute food and aid to those forced out of their homes, the minister added.

Most main roads in state capital Chennai were underwater and trees were uprooted, disrupting traffic.

Residents were seen wading around the city ankle-deep in waters that also lapped up against the century-old offices of the municipal government.

Flooding in Chennai killed more than 250 people during record rainfall in 2015.

Scientists say ever-more unpredictable and extreme weather across South Asia has been caused by climate change and exacerbated by deforestation, damming and excessive development.