London - Passengers were seen badly burned and covered in blood after what police described as a "terrorist incident" on a London Underground train on Friday.The station was closed, as well as an entire section of the District Line where it is located.Ambulances have taken 18 patients to a number of London hospitals. None are thought to be in a serious or life-threatening condition.The Metropolitan Police confirm that they are treating the incident at Parsons Green as a terrorist incident.Burns, stampedes, panicA Metro.co.uk reporter at the scene was quoted by the paper as saying that a white container exploded on the train and passengers had suffered facial burns.She said they were "really badly burned" and their "hair was coming off".Richard Aylmer-Hall said he saw several people injured, apparently trampled as they fled. "There was a woman on the platform who said she had seen a bag, a flash and a bang, so obviously something had gone off," he said. "Some people got pushed over and trampled on, I saw two women being treated by ambulance crews."BBC correspondent Riz Lateef, who was on her way to work, said there was "panic as people rushed from the train, hearing what appeared to be an explosion."People were left with cuts and grazes from trying to flee the scene. There was lots of panic."READ: London tube terrorist attack spooks randOne passenger, named only as Lucas, told BBC 5 Live radio: "I heard a really loud explosion"."I saw people with minor injuries, burnings to the face, arms, legs, multiple casualties," he said.Another witness, Sham, told the radio station he had seen a man with blood all over his face."There were a lot of people limping and covered in blood," he said.London Fire Brigade also said they were at the scene and were called at 8:21 am (07:21 GMT).The Metropolitan Police confirm that they are treating the incident at #ParsonsGreen as a terrorist incident pic.twitter.com/QJLH2nTiV4— Sky News (@SkyNews) September 15, 2017 These photos apparently show what caused the explosion on the #London underground. pic.twitter.com/wFnVztnZrd— Strategic Sentinel (@StratSentinel) September 15, 2017"Police just told us to get out of the area as soon as possible" says witness #ParsonsGreen#LondonUndergroundpic.twitter.com/xqngNPO0aT— Sky News (@SkyNews) September 15, 2017London firefighters are leading passengers off a train along elevated subway tracks. Video from the scene showed people picking their way along the tracks.British Foreign Secretary Boris Johnson says people should "keep calm and go about their normal lives" as emergency services respond to an incident at a London subway station.Johnson says it would be "wrong to speculate," and that police and transit authorities "are on it."The incident comes as tensions are high in London, which has been struck repeatedly by extremist attacks this year.US President Donald Trump is calling a fire at a London subway station another attack "by a loser terrorist" and suggesting police there may have missed an opportunity to prevent it. He also is suggesting that the government cut off internet access to extremist groups.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 Trump tweeted Friday: "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!"He later added: "Loser terrorists must be dealt with in a much tougher manner. The internet is their main recruitment tool which we must cut off & use better!"The London Underground has been targeted several times, notably in July 2005, when suicide bombers blew themselves up on three subway trains and a bus, killing 52 people and themselves. Four more bombers tried a similar attack two weeks later, but their devices failed to fully explode.Last year Damon Smith, a student with an interest in weapons and Islamic extremism, left a knapsack filled with explosives and ball bearings on a London subway train. It failed to explode.In its recent Inspire magazine, al-Qaida urged supporters to target trains.