It's understood no one is seriously injured, although witnesses on social media claimed to have seen one person leave the station on a stretcher.
Specialist police and paramedics rushed to Southgate station and commuters were warned to stay away from the area.
According to information from the British Transport Police and the Metropolitan Police Force, a small number of people have suffered injuries and are being treated on the scene.
"Enquires are ongoing to establish the cause of a reported minor explosion", the Metropolitan Police said on Twitter.
The force tweeted: "Southgate Tube station is now closed whilst officers respond to a suspicious package".
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Meanwhile, border patrol agents are heard cracking jokes about the noise, saying, "Well, we have an orchestra here". Former president Jimmy Carter's wife Rosalynn said the policy was "disgraceful".
"We are not aware of any serious injury", the statement added. I could smell burning (like rubber) and saw multiple people hurrying for the exits.
The Piccadilly line is experiencing severe delays between Arnos Grove and Cockfosters.
"Do not think this is fear mongering or fake news". Suspect device found/gone off inside tube.
A tube station in London is in lockdown after reports of an explosion. "There must be around 50 or 60 police, an ambulance, fire arms and dog units".
Police are now investigating the incident.