Five people have been hospitalised after two cars collided on the Brideswell to Athlone road in Co Roscommon.
The sole occupant of one car, a man aged 23, was seriously injured in the crash which took place at about 4am on Friday morning.
There were two adults and two children (aged two and six) in the second car. All four were taken to Portiuncla Hospital, Ballinasloe, where gardaí on Friday morning said their condition was unknown.
The road is expected to remain closed until lunchtime Friday for a forensic collision examination. Local diversions have been put in place.
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Gardaí asked witnesses to contact Roscommon Garda station on 090 6638300, the Garda Confidential line on 1800 666 111 or any Garda station.