Two people are shot in Philadelphia subway station just hours before Trump and Harris take on debate

Passengers fled for their lives as a gunfight broke out on a busy Philadelphia subway station platform this afternoon as the presidential candidates prepared for their debate just nine blocks away.

At least one person was confirmed shot after a fight escalated on the Market-Frankford Line at Market and 15th streets around 3.30pm.

The city was already swarming with police ahead of tonight's 9pm debate between Kamala Harris and Donald Trump at the nearby National Constitution Center.

A spokesman for the city's SEPTA transport network said a 'small group' of people had been arguing when one pulled out a gun and fired several shots, hitting one of the group in the leg.

Philadelphia police said they had arrested a 17-year-old and recovered a gun from the scene.

His 23-year-old victim was transported to Jefferson Hospital with non-life threatening injuries.

Police said he had also been carrying a gun and is now under arrest.

Local reporter Chris O'Connell of Fox29 said there were reports that a second victim had been struck but that has not been confirmed by police.

The subway station which is directly beneath Philadelphia's City Hall has now re-opened.

Harris has been in the city for several days as she prepares for her faceoff with the former president who was greeted by a phalanx of police officers as he flew in on 'Trump Force One' from his Florida home earlier today.

Philadelphia Police Commissioner Kevin J. Bethel said the city's Office of Emergency Management will be coordinating security arrangements ahead of the debate with both State and federal law enforcement helping secure the area around the event. 

'Our job is to protect both the safety of those individuals participating in the event as well as the individuals who are out and about in the community,' he told a press conference on Monday.