Foreign aid began arriving in Sri Lanka Saturday, bringing help to half a million people forced out of their homes by rains and landslides that have killed at least 71 in a week of extreme weather wreaking havoc in South Asia.

As the heaviest rains in a quarter of a century battered Sri Lanka, Cyclone Roanu barrelled into the Bangladesh coastline leaving six people dead and forcing the evacuation of 500,000 there.

It unleashed winds as strong as 88 kilometres (54 miles) an hour and heavy downpours in Bangladesh after moving away from Sri Lanka's north-eastern coast.

However, the authorities said effects of the cyclone could still bring more rain to Sri Lanka where flood levels were slowly receding.

‘I stayed back on the first floor of a neighbour's flat after my house went underwater,’ said Sri Lankan tea factory worker Kumarage Jayamini, 62, at a welfare centre in a Colombo suburb.

‘The police and the navy persuaded me to leave and they brought me in their boat,’ she told AFP. ‘I am glad I came because otherwise I would have been without food or water.’

Torrential rains have deluged Sri Lanka since last weekend, triggering huge landslides that have buried victims in up to 15 metres (50 feet) of mud and left 127 people missing.

As aid began to arrive Saturday on a military plane from India and a commercial flight from Japan, Sri Lankan authorities said their priority was now preventing diseases such as diarrhoea, with many areas still under water.

‘We have sent a large number of doctors and nursing staff to ensure there is no outbreak of waterborne diseases,’ Health Minister Rajitha Senaratne told AFP.

Irrigation director Prema Hettiarachchi said only the main Kelani river which falls to the Indian Ocean through Colombo was still at flood level, but that too should go down within about three days.

‘If there is no major downpour in the next three days, the flood situation will ease,’ she said.

Residents clung to ropes as they battled to cross torrents of water pulsing through the streets of the flooded capital on Saturday with some forced to take shelter in rickshaws.

The Indian government has provided inflatable boats, outboard motors, diving equipment, medical supplies, electricity generators and sleeping bags, officials said.

Two Indian naval ships arrived Saturday at the port in Colombo, while Australia and the United States have made cash donations to help victims.

- Buddhist holiday -

Nearly 300,000 people were staying in about 500 state-run relief centres Saturday, which also marks the Buddhist holiday of Vesak, while a further 200,000 people were staying with friends or family.

Officials said there was a fresh landslide in the worst-hit central district of Kegalle, but that no casualties were reported because the area had been evacuated.

The country's influential Buddhist clergy urged the faithful to divert at least half of the money spent on holiday celebrations to help flood victims.

‘There are lots of people who have lost their homes, some have only the clothes they are wearing,’ top Buddhist monk Warakagoda Sri Gnanarathana said.

‘Consider this your meritorious deed to celebrate Vesak.’

Vesak celebrations were muted Saturday in Colombo compared with previous years when the entire city was decorated with lanterns and coloured lights.

President Maithripala Sirisena marked Vesak by granting an amnesty and freeing more than 600 prisoners who had been convicted on minor offences, his office said.

He also called on Sri Lankans to provide shelter and donate cash or food to flood victims as offers of assistance came in from overseas.

The accommodation booking website airbnb.com listed at least 29 places offering free lodging for anyone affected by the floods in Sri Lanka.

Disaster management officials said there had been a huge outpouring of sympathy for victims with donations of food, clothing and dry rations.

Around 22 of Sri Lanka's 25 districts have been affected by the rains, according to disaster officials.

Almost a third of residents have been moved from the low-lying capital, which has a population of about 650,000.