Update: 7.25pm: Gardaí believe three men wearing balaclavas were involved in today's shooting in Coolock.
They understand that the three left the scene in a silver Toyota Avensis with a registration number 04-D-71806, which was found burnt out in the Castletymon Gardens area of Coolock at around 3.45pm.
The scene has been preserved for a forensic examination and a post mortem will take place tomorrow.
Gardaí said in a statement: "An incident room has been established at Ballymun Garda Station. Gardaí are appealing for anyone with information to contact them at Ballymun on 01 666 4400, the Garda Confidential Line on 1800 666 111, or any Garda Station.
"Gardaí are particularly interested in speaking to anyone who was in the vicinity of the Kilbarron Avenue or Castletymon Gardens areas of Coolock between 3:15pm and 4pm on 28/05/19, especially road users who may have dash cam footage."
By Cormac O'Keeffe, Security Correspondent
Gardaí believe that a man shot dead in north Dublin this afternoon is an Iranian national and suspected hitman for a major organised crime gang.
The victim, aged in his 40s, is the third man linked to the Finglas-based outfit to have been shot dead in less than a week and the fourth person since January.
The shooting took place on Kilbarron Avenue, in the Kilmore area of Coolock, outside the home of Sean Little.
Little, aged 22, was fatally shot in north county Dublin late on Tuesday last.
Less than 24 hours later, on Wednesday afternoon last, Jordan Davis was shot dead in Darndale, adjacent to Kilmore.
Davis, also aged 22, was pushing his four-month-old son in a buggy, and walking with his partner, when he was shot on a laneway at close range.
Both Little and Davis were friends and drug dealing associates. They, in turn, were friends and associates of Zack Parker, aged 23, who was shot dead in Swords, north Dublin, last January.
They had connections to the Finglas gang, considered to be a major crime outfit across north Dublin.
This gang was, at least until recently, linked to the Kinahan crime cartel, but senior gardaí believe that connection has been severed.
The Iranian national was in the driveway of Little's house at around 3.30pm when a gunman or gunmen opened fire.
The victim was struck a number of times, including to the head, it is thought.
The car that the gunmen travelled in sped away and was found burned out a short distance away at Castletimon Gardens.
Garda sources have stressed that it is not yet known what motive lies behind the various murders, or if they are definitely linked.
Theories being examined include that a rival gang is taking on the Finglas outfit as well as the possibility that some sort of internal feud or row may be behind it.
Local councillor John Lyons called on the Garda Commissioner and the Justice Minister to visit the area and explain to residents how they were going to deal with the escalating violence.
“There is shock in Kilmore West as yet another person was shot dead in broad daylight, the third such shooting on the northside in less than a week,” Cllr Lyons said.
Having visited the area today and spoken to some residents, he said:
“The communities of Darndale and Coolock are reeling from this violence, the vast majority of families living in these areas are trying to live their lives, raise their families and just get on with life. They need to know that the powers that be have a strategy in place to address the rising violence, a plan in place to protect them.”
Update: 4.35pmA man has died in a shooting incident in Dublin.
It has been reported that he was shot in the head.
Local Senator Aodhán Ó Ríordáin says gun crime in Dublin is completely out of control:
Mr Ó Ríordáin said: "This isn't normal. Children shouldn't be growing up in communities where this is happening.
"People are literally being shot and killed in the mid-afternoon. In Dublin's northside we've had shots fired outside shopping centres, we've had pipe bombs, this situation is completely out of control."
The shooting comes a week after two friends were shot dead in north Dublin.
Sean Little and Jordan Davis were shot dead within 24 hours of each other.
Gardaí and emergency services are at the scene of the shooting in the Kilbarron Avenue area of Coolock.
It is understood a man has been critically injured.
It happened at around 3.30pm this afternoon.
The attack comes less than a week after two 22-year-old friends were shot dead in separate attacks nearby.