A 30-year-old woman is dead and her infant has been airlifted to hospital in critical condition following a two-vehicle crash on an expressway west of Kitchener.

It happened on highway 7/8 near Trussler Road in Wilmot, Ont. at around 8:30 p.m., Ontario Provincial Police said.

According to police, one vehicle appears to have rear-ended another.

The woman and her child were travelling in one vehicle, along with two other occupants who sustained minor injuries in the crash, police said.

The woman was rushed to hospital following the crash, where she was eventually pronounced dead. Her three-month-old baby remains in critical condition in a Toronto hospital.

The lone male occupant of the other vehicle was arrested on suspicion of impaired driving, OPP said.

Police are appealing for witnesses in the deadly crash.

The road is expected to be closed until at least 1 a.m. as police investigate.