Cause of the blast remained unknown on Tuesday morning, as investigators turned their focus to the final movements of the vehicle before it exploded

Police were investigating the explosion outside Delhi’s historic Red Fort that killedeight people, with authorities focusing on the final movements of the vehicle allegedly involved.

Police said the explosion occurred around 7pm on Monday evening outside the Red Fort metro station, a peak time when Delhi’s old city is usually packed with people, bustling markets and heavy traffic.

Delhi police commissioner Satish Golcha said the explosion took place after a “slow moving vehicle” stopped at a red light outside the metro station.

Eight people were killed in the blast and around 20 injured. The force of the explosion started a fire that ripped through nearby cars, motorcycles and rickshaws and shattered the windows of a gurdwara, or Sikh place of worship, 500 metres away.