Vietnam is struggling to help communities hit by toxic mudslides after torrential rain in a major coal-mining area in northern Quang Ninh province, home to the UNESCO-listed Halong Bay tourist site.

Quang Ninh was last week hit by the heaviest rain recorded in 40 years, with up to 800 millimetres (31 inches) in some areas, causing flooding, landslides and toxic sludge spills from coal mines.

Seventeen people have been killed, including two families in Mong Duong district who were caught in a toxic mudslide on July 26 which buried the entire community in up to two metres of sludge from a nearby mine.

"In one second, mud and rock smashed into my house. We were lucky to escape with our daughter," To Thi Huyen, 37, a primary school teacher, recalled.

"We have nothing now, as the house and all our assets are in the mud. We don't know what happens next," Huyen told AFP.

Huyen and some 200 other affected people are living in an emergency shelter set up by local authorities in the area.

Pham Ngoc Lu, a local official in Mong Duong, said they were doing their best to help the affected communities.

"We're providing food and other necessities," he said.

Vietnam's famed Halong Bay heritage site is surrounded by thousands of hectares of open-face coal mines and multiple coal-fired power plants.

The torrential rain has caused sludge from the mines to spill onto local communities, creating what activists call immediate and ongoing health and environmental hazards.

"We are deeply concerned by the pace of this unfolding disaster and its sheer scale," said Robert Kennedy, president of Waterkeeper Alliance, an NGO that campaigns for clean drinking water.

At the Mong Duong coal mine, production has been suspended since the rains hit last week. The mine was affected by mudslides, but was not the source of the deluge that hit the nearby community -- which came from another coal mine.

Bulldozers and trucks are working through the night to clear the mud at the mine itself, said company official Tran Quang Canh.

"We're trying to save the mine and recover our production to keep our more than 4,000 labourers employed," Canh said.

Canh said it would take at least 10 days for part of the mine to be brought back into operation, and a further three months to get the mine back to normal production.

The shutdowns at the coal mines in Quang Ninh have prompted state monopoly Electricity of Vietnam to urge the public to save power.

Usually, Vietnam has at least 18 coal power plants in operation, alongside a number of hydro-electric plants.