Heavy rain was falling in Hue, 660 km (410 miles) southeast of Hanoi, swelling floods that have isolated many areas along the north-south Highway One and forcing people to move around by boat, a Reuters photographer said.

At least 30,000 people had been moved to higher ground in the provinces of Thua Thien-Hue and Quang Tri, where two people drowned as their boat capsized on Wednesday, the government said.

Five people drowned in Quang Nam province, many roads were eroded by floods and inundation was threatening to collapse old houses in Hoi An.

The ancient town of Hoi An was designated as a World Heritage site in 1999 by the United Nations Educational, Scientific and Cultural Organization (UNESCO), which describes it as an exceptional example of a Southeast Asian trading port dating from the 15th to the 19th centuries.

Three people, including a two-year-old, drowned in Quang Ngai province to the south of Quang Nam, the government said.

The flood-stricken region is not a significant rice producer, but floods have flushed away farmers' food reserves and the government said it would send 500 tonnes of rice in emergency relief to flood victims in Quang Nam.

The area affected by floods lies north of the Central Highlands coffee belt, where state forecasters said showers were expected on Thursday, two weeks before farmers are due to start their coffee harvest.

The government said flash floods could strike the Central Highland provinces of Dak Lak, Gia Lai and Kontum, which together account for 535,000 tonnes, or 8.92 million bags, of coffee, nearly half of Vietnam's production.

The Daklak government has said a serious dry spell early this year and floods in August could cut Daklak's harvest by up to 8 percent to 6.67 million bags.