A man was arrested after a small blast at a London Underground station believed to have been caused by a faulty drill battery, British Transport Police (BTP) said.
The 23-year-old, from Enfield, north London, was held on suspicion of doing an act likely to cause an explosion to injure or damage property, and endangering safety on the railway.
He has been released under investigation pending further inquiries.
Five people suffered minor injuries after the explosion at Southgate Tube station, BTP said.
Officers were called to reports of an incident shortly after 7pm on Tuesday.
A man on a “packed” escalator said some people had been “trampled” in the commotion.
London Ambulance Service said two people were taken to hospital and three others were treated at the scene.
James Ayton, 34, from Southgate, was on the “packed” escalator when he saw a “quick burst” of flames at the top and said everyone “legged it”.
He said there had been a “very rapid whooshing sound”.
He added: “A few people got trampled on on the escalator. There was screaming.
“An old woman got trampled on. I had to carry a woman up the stairs. I think she was in shock to be honest. She couldn’t walk, shaking.”
London Mayor Sadiq Khan praised the emergency services for “a swift and professional response” to the incident.
BTP confirmed the incident was not believed to be terror-related.
Mick Cash, general secretary of the Rail, Maritime and Transport union said: “Yesterday’s incident reminds us yet again of the need for a full complement of properly trained staff at all stations.
“Whist this incident appears not to be terror-related, the possibility of an attack is always on our minds and safety is our absolute priority at all times.
“It is absolutely right and correct that the Southgate London Underground staff are receiving praise today for their professionalism in the face of another serious incident on the Tube network.”