At least 70 people have been killed and about 200,000 stranded due to landslides and floods in southeast Bangladesh after three days of some of the heaviest rains in the country, officials said.

The army has been deployed to help with search and rescue efforts in the affected hill region of Chittagong, south of the country, said the region's chief administrator, Sirajul Haq Khan on Wednesday, who warned that the toll could rise.

At least 15 people were killed in and around the southeastern port city of Chittagong, while 30 died in Bandarban in an area known as the Chittagong Hill Tracts. A further 24 died in the coastal district of Cox's Bazar near the Myanmar border, officials and police said.

"We are having the worst rainfall in many years," said Jainul Bari, district commissioner for Cox's Bazar.

Chittagong port received 40 centimeters of rain in a single 12-hour on Tuesday.

In Sylhet, north east of the country, houses stood up to one metre under water, leaving residents scrambling to reach higher ground. Three children were reported killed in the area.

According to the state Disaster Management Information Centre, 150,000 people had been marooned by the floods in the southeast while 50,000 in Sylhet were affected by flash floods. Weather officials said more heavy rain was expected over the next few days.