A woman is dead after a fatal crash that has closed the westbound lanes of Highway 401 in Bowmanville this morning.

Original reports suggested the crash — which happened at 4:40 a.m. — was a single-vehicle collision but the OPP has since told CBC News that a tractor-trailer was also involved.

The highway has since reopened.

The OPP say all lanes of Highway  401 between Liberty Street and Waverly Road will likely be closed for several hours.

Police say traffic heading toward Toronto took a detour off the highway at Liberty Street and merged back onto the highway at Waverly Road. The detour caused long delays for westbound drivers. The eastbound lanes were not affected.