Three of them were treated for minor injuries at the scene at Southgate station and two others have been taken to hospital, said London Ambulance Service.
A witness said several people on a packed escalator had been trampled on after the explosion sparked 6ft-high flames.
The blast was thought to have been caused by a battery short circuit, according to the Metropolitan Police.
The station, about eight miles from central London, was closed and the area cordoned off amid reports of a suspicious package.
Police later said the security scare was not believed to be terror related.
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