Videos broadcast on Indian media showed a surge of muddy water sweeping away multi-storey apartment blocks in the tourist region of Dharali in Uttarakhand state.

Pushkar Singh Dhami, Uttarakhand state chief minister, said rescue teams had been deployed "on a war footing".

A local disaster official said at least four people were missing, while others warned the number was likely to rise.

"Luckily, most of the people were at a fair in a safe location," said an official, who asked not to be named since he was not authorised to speak to the media.

India's army said its first teams had reached the town.

"A massive mudslide struck Dharali... triggering a sudden flow of debris and water through the settlement," it said.

Dhami said the flood was caused by a sudden and intense downpour. "News of heavy damage caused by a cloudburst... is extremely sad and distressing," he said.

There were no immediate reports of confirmed casualties.

"I am in constant contact with senior officials, and the situation is being closely monitored," Dhami added in a statement. "I pray to God for everyone's safety."

The India Meteorological Department issued a red alert warning for the area, and recorded "extremely heavy" rainfall of around 21 centimetres (eight inches) in isolated parts of Uttarakhand.

Deadly floods and landslides are common during the monsoon season from June to September but experts say climate change, coupled with urbanisation, is increasing their frequency and severity.

The UN's World Meteorological Organization said last year that increasingly intense floods and droughts are a "distress signal" of what is to come as climate change makes the planet's water cycle ever more unpredictable.