The blast, which happened at around 6.45pm on Wednesday evening, damaged an ULEZ camera in Sidcup.

No one was injured from the explosion, but vehicles and a residential property were damaged.

The Met Police said a "low-sophistication improvised explosive device (IED)" was used to carry out the attack.

"This grotesquely irresponsible behaviour puts both lives and property at risk," Sadiq Khan's spokesman said.

"Police are rightly investigating this dangerous and reckless act."

Counter Terrorism Command officers said that while the incident is not being treated as terrorism, it is believed to have been a "deliberate act".

The camera - installed earlier the same day - was cut down at around 5.15pm, an hour-and-a-half before the explosion, the police said.

Officers are "keeping an open mind as to whether or not there is a connection between the camera being cut down and the planting of the explosive device".

Detective Chief Superintendent Trevor Lawry added: "It is extremely concerning that an explosive device seems to have been deliberately placed in a public place.

"This could have very easily resulted in members of the public being very seriously injured.

"Because of the seriousness of this incident, we are making urgent inquiries to try and identify anyone involved, and officers with specialist expertise and capability from our Counter Terrorism Command are leading the investigation.

"This was an extremely dangerous incident that could have resulted in innocent members of the public being injured or worse."

Read more from Sky News:
LEZ and ULEZ have 'improved London's air quality'
Nearly 1,000 incidents of ULEZ cameras being targeted

Jasmine, who lives in the area and was driving nearby at the time, told Sky News the "explosion was deafening and at first I thought it was some sort of bomb that had gone off".

She added that a van parked nearby was "damaged quite badly" and her car was "covered in debris".

The Ultra Low Emission Zone, introduced with the aim of improving air quality in London, was expanded on 29 August.

Motorists who drive heavily polluting vehicles, usually older or diesel cars, have to pay a £12.50 daily fee to drive in the zone.

The cameras record the movements of vehicles into and around the charging zone.

Mr Khan said expanding ULEZ was a "difficult" but "vital" decision.

Polling from YouGov between 12 to 17 October suggests Londoners are split on ULEZ, with 40% supporting the policy and 40% opposing.

The poll, which surveyed 1,066 Londoners, found 16% neither support nor oppose it.