GUWAHATI/NEW DELHI: Heavy rain hampered the search for 23 Indian troops reported missing on Wednesday after a flash flood in northeastern Sikkim state, with the capital city of Gangtok cut off by road, defence officials said.

"Twenty three personnel have been reported missing and some vehicles are reported submerged under the slush. Search operations are underway," a defence ministry spokesperson said.

India's weather department has warned of landslides and disruption to flights as heavy rain is predicted in some parts of Sikkim.

The main highway linking Sikkim to West Bengal state was snapped and Gangtok was totally cut off by road, according to army spokesperson Anjan Basumatary.

A cloudburst over Lhonak lake was the main trigger for the flooding in the valley located about 150 km (93 miles) north of Gangtok near the border with China.

About 15,000 people living in the vicinity are likely to be affected and at least 8 major bridges have been washed away along the banks of Teesta river, V S Pathak, chief secretary of the state, told Reuters.

Media showed images of the river lashing through the hills and entering human habitations.

Some army bases and facilities along the valley were affected and rising water submerged vehicles following the release of water from a dam, the defence ministry spokesperson based in the neighbouring city of Guwahati said.

Intermittent rain and thunder storms were hampering rescue operations in the area, an army official told Reuters, speaking on condition of anonymity.