The official Disaster Management Centre said Saturday that the death toll from floods and a string of landslides had climbed to 100 while the number of missing since Friday's deluge had been revised down to 90 from 110.

Forty other people are in hospital.

Authorities issued fresh evacuation orders for those living downstream of two major rivers, citing a risk of flooding even though the rains had subsided.

"The monsoon has firmly established and we could have evening showers at a lesser intensity", meterological  department chief S.R. Jayasekera said.

India is sending another ship due to arrive Monday after Sri Lanka issued an international appeal for help.

The flooding is the worst since May 2003 when 250 people were killed and 10,000 homes destroyed after a similarly powerful Southwest monsoon, officials said.

The DMC said the monsoon ended a prolonged drought that had threatened agriculture as well as hydropower generation.

The rains have filled reservoirs used for hydroelectric projects after low supplies had raised fears of power shortages in June.

But officials said most reservoirs were now so full they were in danger of spilling over and flooding communities living downstream.

Friday's flooding was caused by rivers bursting their banks, but unusually heavy rain triggered more than a dozen landslides burying homes on mountain slopes.

By Friday evening over 60,000 people had been driven out of their homes while nearly 500 homes had been either damaged or destroyed.

Most of the deaths have occurred due to mountainsides collapsing on homes, authorities say.