At least 20 people were injured in an explosion at a London train station at around 8:20am on Friday morning (local time).
The explosion took place in a packed carriage towards the rear of a train at Parsons Green station at the height of rush hour.
Police have designated the explosion a "terrorist incident" and said it was caused by the detonation of an improvised explosive device (IED) inside a white container in a bag.
Shortly after the incident a bomb squad was called in to deactivate a second device.
A manhunt for the attacker is underway and police are treating it as a "live investigation", urging Londoners to send in photos and videos of the incident.
A police spokesperson said the train station will remain cordoned off and notified of a heightened police presence throughout the city's public transport system.
Emergency services have confirmed 18 people were hospitalised, most with flash burns.
According to a metro.co.uk reporter people were "really badly burned" and "their hair was coming off".
Witnesses say they saw a large flame before the train filled with smoke, however images of the carriage indicate almost no structural damage.
Heavily armed police attended the scene and evacuated residents in the immediate area. Other nearby homes and businesses were placed on lockdown.
London Mayor Sadiq Khan said the city "will never be intimidated or defeated by terrorism".
"Our city utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life."
UK Prime Minister Theresa May also made a statement following the attack.
"My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terror incident."
Ms May has called for an emergency meeting of top-level security authorities to take place at 1pm Friday (local time).
Scotland Yard’s counter terrorism command, S015, has taken the lead in the investigation which was initially led by British transport police.
Foreign Secretary Boris Johnson appealed for people to remain calm.
He told Sky News: "It really is important not to speculate at the moment. Everybody should keep calm and go about their lives in as normal a way as they possible can. The British Transport Police, TFL are on it. And they will be updating their websites as and when we get more information."
United States Prime Minister Donald Trump has weighed in on the attack, taunting the "loser terrorist" and defending his travel ban.