At least 20 people have been killed and 100 injured by ten bomb blasts that have torn through the main city of India's troubled north-eastern Assam state and two other towns on Thursday.

Local television showed firefighters dousing charred wreckage of vehicles in the state capital Guwhati where, police say, at least four of the blasts occured. Most of the blasts were in crowded markets and the death toll could be more than 20, several TV channels said.

"So far we have got reports of seven people dead, four in Guwahati and three in other towns," a police officer in the main control room of Guwahati said.

Assam has been a focus of a separatist insurgency for decades. Last month, it was also hit by clashes between indigenous tribes and Muslim settlers that left at least 47 people dead.

No one has claimed responsibility as yet for the bomb blasts.

"The impact of the blast was so huge, a packed bus got half burnt and we pulled out lot of injured people and sent them to hospital," Pankaj Goswami, a witness at a blast in Guwahati, said.

In October, at least two people were killed and 100 injured in four bomb blasts that police blamed on Muslim militant groups based in neighbouring Bangladesh.

Dozens of militant separatist groups are active in India's north-east, an isolated region wedged between Bangladesh, Bhutan, China and Myanmar with only a thin corridor connecting it to the rest of India.

Security forces have been fighting a separatist revolt for decades in the state.

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