Five Metropolitan Police officers have been removed from front-line duties after a bag containing firearms and a Taser was left on a London street, the force has said.

The bag, which was discovered by a member of the public on Tuesday evening, was found outside London Mayor Sir Sadiq Khan's home, The Sun reports.

"At this stage it is believed the bag was misplaced by on-duty officers a short time before the member of the public located it," the police said in a statement.

The Met's Directorate of Professional Standards has said it is reviewing the incident.

Inside the bag was a sub-machine gun, a pistol, Taser and some ammunition, according to reports.

The force said: "At around 21:40 BST a member of the public called police after finding a bag containing Met-issued firearms and a Taser on a street in south London.

"Within seven minutes of the call to police, officers arrived at the scene and safely recovered the items.

"We are urgently reviewing the circumstances of this incident and recognise the concern it may cause."

Speaking to The Sun, a passerby saw the bag on the side of a road and alerted her partner after becoming suspicious.

Jordan Griffiths told the newspaper that after looking inside the bag, he took pictures of the contents, then called the police who turned up shortly after.

"When they arrived they were really shocked. They looked through the bag carefully and hurriedly took them away," he told the newspaper.

"I was told they had been left there by one of Sadiq Khan's security officers, which made sense as he lives here."

A spokesperson for Sir Sadiq described the incident as serious, adding: "The Met must now take all steps to ensure an incident like this never occurs again."