A man, woman and two children have been killed while two other youngsters are in a critical condition after a suspected arson attack at a family home in Ireland.
Emergency services rushed to the house in the Birchwood area of Waterford City shortly after 5am on Tuesday.
Police remain at the scene and officers have begun a murder investigation into an attack.
The deaths were confirmed on Tuesday. The two injured children are critically injured in hospital.
One neighbour told the Irish Independent: 'I put in a call at 5.13am. The house was engulfed. It was horrific.'
Another said: 'I must've rang 999 ten times. The big bang woke me up.
'There was an explosion. I could hear screams like in a horror film... it will never leave my mind.'
A third witness said she heard screams coming from the house as it burst into flames after she woke to the sound of her dog barking.
Police at the scene of an overnight fire in the Birchwood estate in Waterford City, Ireland
Emergency services rushed to the house shortly after 5am on Tuesday. Pictured: A police cordon has been set up at the scene
Police have launched a murder investigation and the incident is being treated as a suspected arson attack
When she looked out the window, she saw a cloud of thick black smoke coming from the rear of the property.
She told the Irish Examiner: 'I will never forget what I saw and what I heard for as long as I live.
'I woke from the dog barking and I could hear noises, people screaming and shouting, then I looked out my window and I could see thick black smoke pouring out of the back of the house.
'The sound of the screaming was horrific and I could hear someone shouting, 'Throw the kids down, throw them down.''
Police are now appealing for information. A gardaí spokesman said: 'An Garda Síochána are investigating all the circumstances of a fatal house fire that occurred in the Birchwood area of Waterford City shortly after 5am this morning.
'Gardaí and emergency services remain at the scene.
'An Garda Síochána can confirm two adults, one man and one woman, and two children are deceased.
'Two other children have been removed from the scene and are receiving hospital treatment for critical injuries.
'An incident room has been set up at Waterford Garda Station and a senior investigating officer has been appointed. Family liaison officers have also been appointed.
'An Garda Siochána are appealing for information from anyone who may have been in the vicinity of Birch Avenue, Birchwood, Waterford City in the early hours of Tuesday October 13 to contact Waterford Garda Station on 051 305300, the Garda Confidential Line on 1800 666 111, or any garda station.
'As this is an ongoing evolving incident An Garda Síochána is not in a position to provide any further detail at present.'
Irish minister John Cummins and Taoiseach Micheál Martin paid tribute to those who died.
Mr Martin described it as a 'deeply disturbing situation', and said details of the incident are still unfolding.
Speaking ahead of a cabinet meeting in Dublin, he said: 'Our thoughts and prayers are with anybody who has lost their lives and all who are affected. We thank the first responders who are at the scene.
'We say to everyone to give space to the first responders, to the gardaí to deal with what clearly is a very worrying and deeply disturbing situation.'
Mr Cummins said: 'Waterford has been plunged into utter devastation and sadness this morning with the tragic loss of lives overnight in Birchwood.
'My deepest sympathies go to the loved ones of those who have lost their lives, their friends, neighbours and the wider community.
'I would also like to pay tribute to the emergency services personnel who have been attending what can only be described as a horrific scene.'
The Waterford minister called for gardaí to be given time and space to carry out their investigations.
He added: 'I know that in the difficult days and weeks ahead, the community will rally around those affected, offering strength, compassion and support in whatever way we can.
'At times of unimaginable sadness, it is the kindness and solidarity of a close-knit community that can provide some comfort to those who need it most.
'This is a devastating loss and as a county we stand together in grief and solidarity at this difficult time.'
Bishop Alphonsus Cullinane of Waterford and Lismore expressed his 'profound shock and sorrow'.
'Our hearts go out to the families who suffered such unimaginable loss. We stand in solidarity with all those whose lives have been devastated by this tragedy,' he said in a statement.
Taoiseach Micheál Martin paid tribute to those who died and described the incident as a 'deeply disturbing situation'
In a statement, Waterford Fire Service said it was alerted to a house fire at Birchwood Avenue at 5.13am on Tuesday.
It said: 'A number of units from surrounding stations attended and on arrival found a well-developed fire.
'Firefighting operations commenced immediately, and a number of casualties were removed from the two-storey house.
'The fire was extinguished and the scene handed over to An Garda Síochána.
'Waterford City and County Council has commissioned the Butler Community Centre in St John's Park in Waterford city (X91 FEP4) as a Support Hub.
'Professional supports, refreshments, and facilities are available for those who have been affected by the fire in the Birchwood area.'
Sinn Féin TD for Waterford David Cullinane said: 'This is very raw for everybody involved. My heart is broken.
'I can only imagine what this will be for family members, for the wider family who live right across the road, for the city and county, and for people who live in the housing estate to be dealing with this level of grief and trauma.
'It's just unimaginable, and all we can do at this point in time is to stand in solidarity with the community to support the wider family and this community as much as we can.
'And we're seeing that happen already. My message for this community is that we will be here for you.
'That we understand that this is an unimaginable tragedy, and people may well need to be supported and I'm very clear that that will be put in place.'
Councillor Jason Murphy said the perpetrators of the arson attack in Waterford would face the full rigours of the law.
'We know that it was malicious, which I suppose makes it even worse,' he said.
'I hope whoever those perpetrators are are caught fairly soon and will face the full rigours of the law and that justice will be done.'