The blast took place at a vegetable market in Assam's main city of Guwahati, a police official said.

"The blast was of a very high magnitude, killing five people on the spot. The dead include an infant of about six to seven months old," police officer Rajen Singh told AFP.

A man critically injured in the blast died at the hospital on Saturday, a police spokesman said, taking the toll to six.

At least 12 people were also injured in the explosion, most of them either shoppers or vendors.

A doctor at the Guwahati Medical College Hospital, where the injured were taken, said several people are listed as critical with multiple wounds in their chest, face and abdomen.

Police said it was likely the blast had been carried out by the outlawed United Liberation Front of Asom (Ulfa), a rebel group fighting for an independent homeland for more than three decades.

The Ulfa was also blamed for a string of ethnic attacks in January that killed 80 people in eastern Assam.

More than 10,000 people have lost their lives to insurgency in Assam during the past two decades.