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 will investigate.

Divya Raghavendra Rao, co-founder and managing director of the cafe chain, said she was told there were two explosions within 10 seconds of each other, injuring one customer and three employees.

"It was nothing in the kitchen that exploded, it happened in the area where customers wash their hands ... something that was kept in a bag exploded," Rao told the local TV9 news channel, adding that all the injured were out of danger.

The cafe had given its CCTV footage to help police investigate the cause of the blast, she said.

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 TV9.

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% burn injuries and was in intensive care. (Reporting by Indranil Sarkar and Varun Vyas in Bengaluru and Tanvi Mehta in New Delhi; Writing by YP Rajesh and Shivam Patel; Editing by Alison Williams)