A truck is believed to have jackknifed on the N4 motorway between Boyle and Carrick-on-Shannon, in Co Roscommon, at around 8.30am.
Three cars are understood to have struck the lorry, while two people are reported to have been injured and taken to Sligo University Hospital. The road has since been closed.
Icy conditions have hampered motorists in the area.
AA Roadwatch said: “The N4 is closed both ways on the Boyle side of Carrick-on-Shannon due to a collision.
“Gardai advise extreme care due to slippery conditions in the area.”