A villager uses a makeshirt raft to transport relatives through floodwaters in Bartezpur village, Guwahati on September 23, 2014.

The chief minister of the northeastern state of Meghalaya, where 35 people have died, said the floods were the worst in recent memory, and bad weather was hampering the rescue effort.

"So far, 35 people have died in separate cases of drowning and landslides in the last two days with more than 20 more still missing," Meghalaya chief minister Mukul Sangma told journalists.

"We have put the entire region on a state of maximum alert."

Adjoining Assam state is also on high alert after 20 people died in separate incidents of drowning and mudslides during three days of heavy rains.

Floods have hit several parts of Assam, with the main city of Guwahati particularly hard hit.

"Five people have died in Guwahati alone in separate incidents of mudslides and electrocution after neck-deep floodwaters submerged localities," district magistrate Anga Mathu said.

Hundreds of people have been forced up onto their roofs or even into the trees to escape the raging waters, one local community leader said.

Authorities in Assam estimate that 350,000 people have been forced to leave their homes due to floods.

"We are taking all relief and rescue measures in the flood-hit districts," said Assam chief minister Tarun Gogoi.

Floods and landslides hit South Asia every year during the monsoon season. This year hundreds of people were killed and many more left homeless after devastating flooding in the Indian state of Kashmir.