At least eight people have been killed in a car explosion near the Red Fort in the Indian capital territory of Delhi, police say.

Local television channels reported at least 20 people were wounded in the blast on Monday.

It was not immediately clear what caused the explosion close to the Red Fort metro station.

The neighbouring Uttar Pradesh region and India’s financial capital, Mumbai, were placed on high security alert in the wake of the incident, Indian media reported. So too were nearby sites including Indira Gandhi International Airport, according to a statement by India’s central police force.

In videos shared online, the wreckage of several cars could be seen on a congested street in the old quarter of Delhi as police poured into the area to secure it and push back gathering crowds.

The explosion caused six vehicles and three autorickshaws to catch fire, according to New Delhi’s deputy fire chief.

Delhi Police Commissioner Satish Golcha said the blast happened shortly before 7pm (13:30 GMT).

“A slow-moving vehicle stopped at a red light. An explosion happened in that vehicle, and due to the explosion, nearby vehicles were also damaged,” he told reporters, adding that the situation was being monitored.

Indian Home Minister Amit Shah promised an in-depth probe into the incident.

“We are exploring all possibilities and will conduct a thorough investigation, taking all possibilities into account. All options will be investigated immediately and we will present the results to the public,” Shah said.

The home minister confirmed that he would visit the site of the blast as well as the hospital where victims were taken.

The 17th-century Red Fort, which was formerly an imperial palace, is a major tourist attraction.

Speaking to Al Jazeera, independent journalist Amit Baruah described the area as “one of the most crowded parts of the city”, something he said made it “vulnerable” to attacks.

“It shatters the calm of the capital city,” said Baruah, who noted that Delhi had not experienced a blast like Monday’s in recent memory.

“This is an incident that will definitely cause concern to ordinary people living not just in that area but around,” he noted.

Indian Prime Minister Narendra Modi offered his sympathies to the families of the victims.

“Condolences to those who have lost their loved ones in the blast in Delhi earlier this evening. May the injured recover at the earliest,” Modi wrote on X.