A murder investigation has been launched following the deaths of four people after a house fire in County Waterford, Gardaí (Irish police) have said.

Two children and two adults – a man and a woman – died following the blaze on Birch Avenue, on the outskirts of Waterford city, shortly after 05:00 local time on Tuesday.

Two other children have been critically injured and they are being treated in hospital.

Gardaí said they were investigating the fire as arson and appealed to anyone who was in the vicinity in the early hours of Tuesday to contact them.

Waterford Fire Service said it was alerted to the fire at 05:13 local time and its crews arrived to a well-developed fire at a two-storey house.

It said a number of casualties were removed from the house before the blaze was extinguished and the scene was handed over to gardaí.

Gardaí have set up an incident room at Waterford Garda Station and a senior investigating officer had been deployed to the incident.

Family liaison officers had also been appointed.

The housing estate is just off the Killure Road, about 3km (1.8 miles) outside Waterford city centre.

Sinn Féin’s David Cullinane, who represents Waterford in the Dáil (Irish Parliament), said he knew the family and said his heart went out to their relatives.

“I’m just utterly heartbroken,” Cullinane said.

“There is such devastation in the housing estate itself but also in the wider community in Waterford city.”

His party colleague, Sinn Féin councillor John Hearne, also knows the family and described it as a “terrible tragedy”.

Hearne told BBC News NI that residents living in the estate noticed the blaze at about 05:00 and they went out to wake up their neighbours to try to help.

But he said it “all happened so fast” and was “hugely distressing for everyone involved”.

The councillor said the estate had been blocked off by gardaí but he planned to go to the community centre later where the council had set up a support hub.

Waterford City and County Council said facilities and refreshments were available at Butler Community Centre in St John’s Park for anyone affected by the fire.

The Bishop of Waterford and Lismore, Alphonsus Cullinan, described it as an “unspeakable tragedy” which had shocked the entire city.

In a statement, he said: “Our hearts go out to the families who have suffered such unimaginable loss.

“We stand in solidarity with all those whose lives have been devastated”, he added.

He said the Catholic Church would “reach out as best we can” to help those affected and the parish priest would minister to the bereaved family and support the local community.

“We also wish to express our sincere gratitude to the emergency services, gardaí, firefighters and medical personnel who responded to the scene and who have faced such distressing circumstances,” the bishop added.

The mayor of the Waterford Metropolitan District, Lola O’Sullivan, urged people not to speculate about the cause of the fire.

“It upsets me no end to see people commenting on social media about something that they don’t have firm facts on,” she said.