At least 17 people have been killed by heavy rains and flooding in the northeastern Indian state of Assam, while at least 14 people have died in Bangladesh, with millions of people also displaced, officials said on Saturday.

Persistent heavy rains this week have caused widespread disruption across South Asia, with at least 68 people killed in Nepal by flash floods and landslides.

Although rainfall had decreased as of Saturday, officials in Assam, a tea-growing and oil-rich state, added water levels across rivers were still overflowing.

"Overflowing rivers are flooding new areas, making things worse," said Keshab Mahanta, Assam's water resource minister.

India's Interior Minister Rajnath Singh was due to visit Assam on Saturday and make an aerial survey and hold discussions with state officials about relief efforts.

Authorities in Assam have opened more than 800 temporary shelters and food and medicines distribution centers across the state, a senior official at the state disaster management authority said.

Flooding is an annual problem during the monsoon season in South Asia, but the impact has been worsened by crumbling civic infrastructure, clogged drains and uncontrolled urban expansion.