The N2 road at Emyvale is set to remain closed until approximately 8pm this evening following a serious collision yesterday.
The road remains closed to allow for a technical examination of the scene and diversions are in place, with traffic travelling between Monaghan and Aughnacloy being diverted via Middletown and Caledon.
The crash, which involved a van and a lorry, happened at around 3.40pm yesterday at Lisseagh during which a man was injured.
The driver of the van, a man in his 40s, was airlifted to Tallaght Hospital where his condition is understood to be serious.
The driver of the lorry escaped injury.
Emergency services, including the Monaghan Fire Service, responded to the scene.
Gardaí in Monaghan are appealing for anyone with information to contact 047-77200 or the Garda confidential line.