Police say a medical condition could be to blame for a massive chain reaction crash on the Pat Bay Highway that sent three people to hospital and closed the route for hours Tuesday.

It started when a vehicle travelling northbound on the highway struck a car turning on to East Saanich Road at around 7 p.m., according to police.

That set off a series of collisions in the intersection including one between a truck and a car.

One of the occupants of the truck was taken to hospital with serious injuries and two others were also transported to hospital.

In all, four vehicles were involved in the crash in the intersection – but the mayhem didn’t end there.

Police said the vehicle that caused the crash drove on to Sidney, where it crashed into another car.

The man was eventually stopped by police and taken to Saanich Peninsula Hospital.

Police said the driver may have been suffering from a pre-existing medical condition but didn't confirm what it might have been.

An investigation into what went wrong is ongoing.