London has faced its fifth attack by terrorists in 2017, when a homemade bomb device exploded on a packed London commuter train during rush-hour.

The explosion occurred at 8:20am on Friday (local time), and 29 were injured when fire engulfed a carriage at Parsons Green underground station in West London.

Following the incident at #ParsonsGreen this morning we have taken 19 patients, mostly with minor injuries to three London hospitals. pic.twitter.com/1Y3dpTJifA

— London Ambulance (@Ldn_Ambulance) September 15, 2017

The ambulance service reports none of the injured passengers were thought to be in a serious condition. Some suffered burns while others were injured in a stampede to escape the train and the station.

One woman – who only identified herself as Lauren to reporters – said the crowd “panicked” when they saw the fireball ripping through the train’s carriage.

Passengers sustained burn injuries while others were injured during a stampede to escape the station. Image via Getty.

"It was this flame of orange coming towards you," she told reporters.

"We just panicked... and we ran in the opposite direction."

To the man that pulled me out of the pile of people on the stairs during the stampede at Parsons Green - thank you. Thank you so much.

— Katherine Manson (@KatherineManson) September 15, 2017

Passengers were only able to escape due to the fact the train was stationary at the time of the explosion.

"I am just so glad that it happened when the tube was stationary. Everyone would have been engulfed otherwise," she said.

Pictures taken at the scene showed a white bucket with a supermarket freezer bag on the floor of one train carriage. The bucket was in flames and there appeared to be wires coming out of the top.

#ParsonsGreen: These unverified images will form part of the police's investigation. Second pic via Sylvain Pennec https://t.co/zQnRgUYM0n pic.twitter.com/otkY5LRdXs

— Sky News (@SkyNews) September 15, 2017

"We now assess that this was a detonation of an improvised explosive device," Britain's top counter-terrorism officer Mark Rowley told reporters.

Prime Minister Theresa May called the incident a "cowardly attack" and said the national threat level had been raised to its highest level, "critical".

"My thoughts are with those injured at Parsons Green and the emergency services who, once again, are responding swiftly and bravely to a suspected terrorist incident," May said.

"This was a device intended to cause significant harm."

She wasn't the only world leader to condemn the attack.

"Another attack in London by a loser terrorist," US President Donald Trump said on Twitter.

Another attack in London by a loser terrorist.These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!

— Donald J. Trump (@realDonaldTrump) September 15, 2017

"These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!"

A manhunt is underway to find the person responsible.

With AAP.

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