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 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 is being detoured off the highway at Liberty Street and merging back on to the highway at Waverly Road. The detour is causing long delays for wesbound drivers. The eastbound lanes are not affected.