THIS is the moment the Londonderry car bomb exploded in the city centre last night.

Armed New IRA terrorists planted the explosives in a hijacked pizza delivery car, police say, in an attack described as a "very significant attempt to kill people in the community."

14 PSNI released CCTV footage of the car parked outside the courthouse last night Credit: PSNI

14 At 8.09pm, the bomb explodes in an enormous fireball Credit: PSNI

Police said they had now arrested four men in connection with the blast.

Two men in their 20s were arrested in the city in the early hours of Sunday by detectives investigating the explosion.

Later two men, aged 34 and 42 years were arrested in the city.

PSNI Assistant Chief Constable Mark Hamilton made the comments during an interview with Sky News.

He said the stolen vehicle, a Ford Fusion, was driven through the city centre with a "crude" and "very unstable" bomb planted inside — which could have gone off at any time.

Hamilton said the pizza delivery vehicle was hijacked by "at least two armed men" who may belong to the New IRA (previously known as the Real IRA).

After a man placed the bomb inside the car, a call was made to the Samaritans which was then referred to the police.

Emergency services raced to the scene and began evacuating the area just in time.

The bomb detonated outside a courthouse on Bishop Street at around 8.15pm — just as police were leaving.

A cordon remains in place today at the site of the explosion.

The PSNI added: "As far as we know no one injured. There is another car we are not happy about. There are ongoing necessary evacuations."

Witnesses say they heard a loud bang and a large plume of smoke.

Several bars and houses were evacuated, but there has been no reports of casualties so far.

DUP MLA Gary Middleton, and former deputy mayor of Londonderry, wrote on Twitter: "PSNI have confirmed there were no injuries in the serious incident at Bishops Street. Vehicle hijacked with explosion outside courthouse. Disgraceful act of terrorism."

He added: "Deeply disturbing. A throwback to the past. I hope there are no injuries or fatalities."

"This pointless act of terror must be condemned in the strongest terms. Grateful to our emergency services for their swift actions which helped ensure there have been no fatalities or injuries," DUP leader Arlene Foster said on Twitter.

SDLP Foyle MLA Mark H Durkan said: "Whoever is responsible for this explosion within our city centre hasn’t got the message that the people of Derry don’t want this on our streets.

'NO ONE WANTS THIS'

"Whatever their agenda is they are causing distress, damage and potential death and that is not the way to further your cause."

Fiachra McGuiness, a son of the late former deputy first minister Martin McGuinness, wrote on Twitter: "Whoever is responsible for this bomb in our Beautiful City tonight, live in Planet hate."

Alliance party leader Naomi Long MLA wrote on Twitter: "Very disturbing news from L-Derry this evening. Hope that no-one is hurt. Police now reporting a second suspicious vehicle in the area."

Sinn Fein MP Elisha McCallion condemned the possible car bomb attack.

The Foyle MP said: "This incident has shocked the local community.

"In particular, there are many elderly residents who live in the area who have been alarmed by this incident.

"Thankfully no one appears to have been injured in this incident.

"Derry is a city moving forward and no one wants this type of incident. It is not representative of the city.

"I would encourage anyone with information about this incident to bring it to the police."

The New IRA was behind the last such fatal attack when in 2016 a prison officer was seriously injured when a bomb exploded under his van in Belfast. He later died from his injuries.

In Londonderry, police and fire officers came under petrol bomb and missile attack for a number of nights last July from Catholic youths in the Bogside area of the city around the time of annual parades that often raise tensions.

The bombing comes as police on both sides of the now-open border between Northern Ireland and European Union-member Ireland have expressed fears that a return to a hard border after Brexit, complete with customs and other checks, could be a target for militant groups.

14 Police on the scene on Bishops Street Credit: Reuters

14 One of the clips released by police shows a man leave the car and run away shortly before the explosion Credit: PSNI

14 While another shows a large group of people passing right by the lethal device minutes before it blows up Credit: PSNI

14 An investigator with the twisted wreckage of the van used in a car bombing in Londonderry Credit: Getty Images - Getty

14 Forensic teams at the scene earlier today Credit: Pacemaker Press

14 A fire in the wake of the explosion last night Credit: AFP or licensors

14 The scene of the car bomb in Londonderry city centre Credit: PA:Press Association

14 An ambulance was seen on Bishop St but it is thought no one was injured Credit: PA:Press Association

14 The wreckage of the vehicle could be clearly seen Credit: PA:Press Association

14 A small crowd gathered at the scene as the police sealed off the area Credit: PA:Press Association

14 Police sealed off the area and evacuated pubs and homes Credit: PA:Press Association

14 The blast occurred at around 8.15pm last night Credit: PA:Press Association

PSNI have confirmed there were no injuries in the serious incident at Bishops Street. Vehicle hijacked with explosion outside courthouse. Disgraceful act of terrorism. pic.twitter.com/X0YoUT7ZUb — Gary Middleton MLA (@Gary_Middleton) January 19, 2019

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Britain is due to leave the bloc in less than 10 weeks, with the future of the border at the centre of its difficulties to strike an amicable divorce deal.

The British and Irish governments, which are co-guarantors of the 1998 peace deal, expressed concern at the incident.

"There is no place and no justification possible for such acts of terror, which seek to drag Northern Ireland back to violence and conflict," Irish Foreign Minister Simon Coveney said on Twitter.