At least four people were injured in a blast at a cafe in India's technology hub of Bengaluru on Friday, police said.

The blast at Rameshwaram Cafe in the east of the city occurred during the busy lunch hour when crowds from nearby offices line up.

The cause of the blast was not immediately known, a policeman at the site said, adding that a bomb squad was on its way to investigate.

Television footage showed a pillar inside the cafe damaged from the impact of the explosion.

"I heard a loud sound and rushed to the spot and could see some smoke," Shabarish, a witness, told the local TV9 news channel.

Some people had injuries on their arms and legs, and identification cards were strewn around the cafe in the chaos, he added. Television channels reported at least five had been injured, but there was no immediate confirmation from police.

Three of those injured were taken to a hospital nearby where staff said two of them had suffered minor injures. The third had 40 per cent burn injuries and was in intensive care.