Terror threat level raised to critical following Parsons Green Tube bomb, May

Britain's Prime Minister Theresa May leaves 10 Downing Street to attend Prime Minister's Questions, in London, September 13, 2017. REUTERS/Peter Nicholls
The terror threat level has been raised from severe to critical following the Parsons Green Tube bomb, PM Theresa May said.

The UK terror threat has been increased to the highest level following the attack on a Tube train in south-west London, the prime minister has said.

Theresa May said the threat had been upgraded from severe to critical – meaning an attack is expected imminently.

An explosion has occurred at a London subway station, leaving several passengers injured. The blast took place on a rush-hour underground train at the Parsons Green station in west London, shutting down a district subway line.

There are reports of multiple casualties and victims with burnt faces. Witnesses also say that a stampede followed the incident, injuring more people before the police and paramedics arrived.

The Metropolitan and British Transport Police say they are aware of the incident, confirming that armed forces are present on the ground to investigate the case.

They also advised people to avoid the area, but made no further comments about the possible casualties or the cause of the incident.