The winter monsoon has caused flooding across a third of Sri Lanka [EPA]

The death toll from flooding across a third of Sri Lanka has risen to 23 people, and another 100,000 people have been forced from their homes as heavy monsoon rains lashed the island and threatened food supplies.   

The agricultural ministry said at least 21 per cent of Sri  Lanka's staple rice crop had been destroyed, raising concerns over supply shocks and higher food inflation just as the  central bank lowered lending rates to spur growth.   

Greater-than-normal monsoon rains since early January have pounded Sri Lanka's Northern, Eastern, Central and North  Central provinces, setting off mudslides, swamping roads and bursting hundreds of dams and reservoirs.   

In the hardest-hit area, the eastern port of Batticaloa, rainfall since the beginning of January stood at 1.8 metres, more than its average annual rainfall of 1.6  metres, S R Jayasekera, the meteorology department deputy director, said.   

"About 161,878 hectares of paddy lands are under water and it is still too early to estimate the extent of damage. If the water subsides in the next two-three days we might able to recover 30 per cent of it," Mahinda Yapa  Abeywardene, the agriculture minister, told Reuters.

Sri Lanka depends on monsoon rains for irrigation and power generation, but the seasonal downpours frequently cause deaths and damage property in low-lying areas.

The island's two main monsoon seasons run from May to September and December to February.