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 be caused by a battery short circuit, according to the Metropolitan Police.
The station, about eight miles from central London, was closed and the incident came as officers investigated a suspicious package.
Police said the security scare was not terror related.
James Ayton, 34, from Southgate, was on an escalator when he saw a “quick burst” of flames at the top.
He said the flames were “6ft plus” and everyone “legged it”. Mr Ayton said: “It wasn’t a bang. It was like a very rapid whooshing sound.”
He said the escalator was “packed”, adding: “The Tube had just unloaded. The escalator was full.”
Mr Ayton said: “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.”
Twitter user Salamander_Sean said he saw one person being taken out on a stretcher.
He wrote: “We have been told to stay inside. Suspect device found/gone off inside tube. Saw one person coming out on a stretcher.”
Haluk Ozkan, who lives near Southgate, had been waiting for a bus when there was a burning smell.
Speaking to Sky News, he described the smell as “like a rubbery burning, quite distinct”.
“We thought that it would be the bus engine or wheel spins being done by a car or something. But it obviously wasn’t that, knowing what we know now.”
He said: “We looked into the station and could see people scurrying, not running. There was no panic that I could see.”
He added: “My partner saw a staff member (inside the station) grab the extinguisher to put something out.
“We didn’t see what it was. It was obviously some sort of fire.”
Darren Yarlett, 36, was driving home in Southgate but police had cordoned off roads near the station.
He told the Standard: “The police moved us on, but they said there was an explosion in the station.
“There must be around 50 or 60 police, an ambulance, fire arms and dog units.”
He added: “I didn’t hear anything so don’t want to jump to any conclusions but the amount of ambulances would say something has happened.”
A spokeswoman for London Ambulance Service said: “We were called today at 7.02pm to an incident at Station Parade, N14.
“We sent multiple resources to the scene, including a number of ambulance crews, our hazardous area response team, a medic in a fast response car, an advanced paramedic and an incident response officer.
“We have treated three patients at the scene for minor injuries and have taken two people to hospital.”
British Transport Police tweeted: “Southgate Tube station is currently closed whilst officers respond to a suspicious package.
It later wrote: “Officers from @BTP & @metpoliceuk remain at Southgate Tube station following an earlier incident.
“Enquiries continue but we do not believe this to be terror related at this time.”
The Met said in a statement: “Police were called at 7.03pm on 19 June to reports of an explosion and people running at Southgate underground station.
“Met officers attended the scene along with colleagues from British Transport Police (BTP), London Fire Brigade and London Ambulance Service.
“The scene has been examined by specialist officers. It appears at this stage that the cause of the explosion was a battery short circuit. The Met Police and BTP are working together to establish the full facts.”