Three were treated for minor injuries at the scene at Southgate station and two others have been taken to hospital, said London Ambulance Service.
The station has been closed and the incident comes as officers investigated a suspicious package.
Police said they did not believe the security scare was terror related at this time.
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 said: “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.”
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 Metropolitan Police 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 remain at the scene along with colleagues from British Transport Police, London Fire Brigade and London Ambulance Service.
“Cordons are in place and the station is closed.”
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.”