Parts of London’s Heathrow Airport were briefly locked down on Sunday after a man assaulted a group of people with pepper spray after an argument.

Police said that the man was arrested, adding that the incident was not being treated as a case of terrorism, reported news agency AFP.

The incident occurred at Terminal 3’s multi-storey car park of the Europe’s busiest airport after an argument between “a group of people known to each other”, London’s Metropolitan Police said.

The authorities said 21 people were being treated at the scene and five were taken to the hospital, while the suspect was taken into custody.

Police said all the injuries were “not believed to be life-changing or life-threatening”.

Incident leads to brief panic, traffic chaos

London’s Metropolitan Police said they received a call around 8:00 am (local time) of multiple people being assaulted in the parking.

“A number of people were sprayed with what is believed to be a form of pepper spray by a group of men who then left the scene,” the police said.

“Armed response officers attended and arrested one man on suspicion of assault. He remains in custody and enquiries continue to trace further suspects,” the police added.

While a man was taken into custody on suspicion of assault, a search is on for other suspects who left the scene.

The incident prompted a brief scare as train lines in and out of the airport were stopped for more than an hour, according to a New York Times report.

The police officers, meanwhile, halted car and foot traffic into and out of certain parts of the terminal complex, leading to severe traffic disruption in the area. However, an AFP report said that Terminal 3 remained open throughout.

The airport issued an advisory urging passengers to reach the airport well in advance due to traffic congestion.