NEW DELHI -- Eight people among those who were brought to a hospital after a blast in Delhi died on Monday evening, the hospital's medical superintendent confirmed.

A total of seven injured people were still in the hospital, and three of them were in critical condition.

The blast occurred inside a car near the historic monument Red Fort. According to police, a slow-moving vehicle stopped at the red light on the road, and then a blast took place. The explosion triggered a fire in nearby vehicles, damaging nearly two dozens.

Immediately after the blast, firefighters, police teams and forensic experts reached the spot to investigate the blast.

India's premier terror probe agency, National Investigation Agency (NIA), and the National Security Guard (NSG) joined the investigation.

"Following the deadly explosion outside Delhi's Red Fort metro station on Monday evening, a high alert across the national capital has been sounded. India's commercial capital, Mumbai, too, has been placed on heightened vigilance following the blast in Delhi," the India Today TV channel said.

"The blast in Delhi has prompted authorities in several cities and states, including Kolkata, Dehradun, Haryana, and Uttar Pradesh, to declare an alert and intensify security measures."

Another TV channel NDTV put the death toll at 13.

Indian Prime Minister Narendra Modi condoled the deaths. Home Minister Amit Shah visited the hospital where the injured were admitted.

Bomb squads and forensic teams reached the spot to ascertain the nature of the explosives used in the blast. Efforts were also made to trace the owner of the car used in the blast.