At least nine people were killed, thousands of homes damaged and swathes of farmland flooded as Typhoon Kai-Tak swept across northern Vietnam, authorities said Sunday.

The storm, which made landfall late Friday, brought strong winds and heavy rains that inundated several densely populated communities including part of the capital Hanoi.

Five people were swept away by floodwaters while one woman died when a landslide buried her house while she was sleeping in Bac Giang province, according to the government's central committee on flood and storm control.

A taxi driver was killed by a toppled tree while two people were electrocuted by a falling electricity cable, it said.

Nearly 12,000 houses were damaged and 23,000 hectares (56,800 acres) of cropland were flooded, according to the committee.

In Hanoi, about 200 large trees were uprooted and part of the city remained under water early Sunday.

The Vietnamese army had put 20,000 soldiers backed by helicopters, rescue boats and canoes on standby for rescue operations, but only a small number of them were deployed.

More than 11,000 boats, including several hundred used by tourists at the UNESCO world heritage site Halong Bay, were ordered to stay close to the shore.

The storm, which earlier killed four people in the Philippines, was packing winds of about 100 kilometres (62 miles) per hour when it slammed into Vietnam, but it was downgraded to a tropical depression on Saturday.