A pregnant woman, her two-year-old daughter and two other young children have died after a fire in west Dublin.

27-year-old Annmarie O'Brien and her two-year-old daughter Paris were pronounced dead at Tallaght Hospital shortly after the fire in an apartment in Clondalkin in the early hours of this morning.

Three-year old Holly was also pronounced dead at Tallaght Hospital.

Her brother, four-year-old Jordan, was pronounced dead at Our Lady's Hospital, Crumlin late this afternoon. 

Holly and Jordan's mother, Biddy O'Brien, is in a critical condition at St James's Hospital.

The cause of the fire has not been confirmed but it is believed it was accidental, possibly due to an electrical fault.

The apartment building is supported housing for women who have experienced domestic violence.

Emergency services attended the scene of the fire at Cluainin Cronan, Clondalkin at about 2.30am.

Five people were in the first-floor apartment at the time of the fire.

There are three other apartments in the building and residents were removed for their safety. Two were brought to hospital as a precaution to be assessed for the effects of smoke inhalation.

President Michael D Higgins has expressed his sympathies to those affected.

Speaking at Áras an Uachtaráin at a reception for International Women's Day, President Higgins said: "I want to express my sympathy to all of those affected by the tragedy in Clondalkin.

The women involved would have been represented here today. All of our hearts must go out to these women and children.

Gardaí are examining the scene of the fire.

A spokesman for Dublin Fire Brigade said a number of emergency calls were made about the blaze, with the first alert coming in at 2.33am. It is understood the first crews were on the scene within five minutes.

Clondalkin, Dublin

"We got numerous calls in about it which would indicate that the fire was noticeable. The fire alarm in the apartment had also gone off," a spokesman said.

Domestic violence charity Sonas, which runs the supported housing in the complex, has said it is devastated by the fire.

Sonas CEO Fiona Ryan said: "Our sympathies and condolences are with the relatives and friends of the deceased and all those impacted by this awful tragedy."

She added: "We are currently supporting other families in the apartment complex including those unable to return to their homes because of fire damage for whom we are sourcing alternative accommodation.

"We would ask that the privacy of all families residing in this complex be respected at this time of loss."

Speaking on RTÉ's Drivetime, Ms Ryan said: "Right now, we are focusing on putting our own emotions aside and we are focusing on supporting the other families in this complex, around their emotional needs, but also surrounding their practical needs.

"We have to provide alternative accommodation for three other families at relatively short notice and we were able to do that through a combination of luck and good fortune." 

Separately, four people were injured and several others were rescued following a fire at an apartment in Dominick Street in Dublin.

Three of the four were treated for smoke inhalation. The fire broke out around 3am.

Four units of Dublin Fire Brigade attended the scene of the fire, which was later brought under control.