A car explosion in the bustling heart of the Indian capital on Monday killed at least eight people and injured another 19, officials said.

Police have not given details on the cause, but said that forensic and anti-terrorism agencies were at the site, near the landmark Red Fort.

Prime Minister Narendra Modi offered his condolences to the families of those killed, and said he had "reviewed the situation" with Home Minister Amit Shah and other officials.

"Condolences to those who have lost their loved ones in the blast in Delhi...may the injured recover at the earliest", Modi said in a statement. "Those affected are being assisted by authorities."

The blast took place in the early evening as people returned from work, close to a metro station in the crowded Old Delhi quarter of the city.

Ambulances streamed into a nearby public hospital, carrying several injured people, AFP reporters said.

Citing authorities at the hospital, New Delhi's deputy chief fire officer AK Malik told AFP that "eight people have died so far and 19 are injured."

'Heartbreaking'

The capital's Police Commissioner Satish Golcha told reporters that "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."

AFP photographers at the site saw pools of blood spattered across the road.

At the city's LNJP hospital, the emergency ward was chaotic as injured people streamed in and doctors rushed to attend to them. 

A woman broke down outside the ward where her husband was being treated. 

"I can't bear to see him like that," she said, as her brother tried to console her.

Opposition leader Rahul Gandhi said in a statement that the "news of the car explosion near Delhi's Red Fort Metro Station is extremely heartbreaking".

The blaze engulfed at least six cars and several motorised rickshaw taxis.

The nearby hospital building was cordoned off amid a heavy police deployment as officers moved through the corridors.

Outside, anxious relatives gathered after hearing that their loved ones had been brought in.

Musarrat Ansari said her brother was injured after a burning car hit the motorbike he was riding.

"He called me and said his leg was hurt -- he couldn't walk," she told AFP.

The Red Fort, which was completed under Moghul rule in 1648, is one of India's most well-known landmarks.

Indian prime ministers address the nation from its ramparts on Independence Day, and it features on the largest banknote.