A car explosion killed at least 10 people near a metro station at the landmark Red Fort monument in Delhi, India, on Monday.

More than 30 other people were “badly injured” in the blast, said Dr. Manish Kumar Jha, a physician at the local Lok Nayak Hospital. “Many are not in a position of recovering,” he told reporters.

While the cause of the blast is not yet known, airports, railway stations, government buildings and heritage sites across the country have been put on high alert, according to the Central Industrial Security Force.

The Red Fort, known in India as the Lal Qila, is a 17th-century Mughal-era fort in the old city and visited by tourists throughout the year.

Before the explosion, a “slow-moving” vehicle “came to a stop” near a red light around 6:42 p.m. local time (5:42 a.m. ET), Delhi Police Commissioner Satish Golcha told reporters.

“An explosion occurred in that vehicle. The passengers in the vehicle and people in surrounding vehicles were impacted,” Golcha said. At least six vehicles and three autorickshaws were set on fire, Reuters reported, citing Delhi’s deputy fire chief.

Emergency crews then arrived at the scene and extinguished the blaze – after receiving a call at 6:55 p.m. local time (5:55 a.m. ET), Sumit Kumar, a Delhi fire services official, told CNN. Survivors were taken to a nearby hospital