An overnight crash on a northwestern Ontario highway sent two people to hospital in Thunder Bay and closed the main route into Sioux Lookout for over 12 hours.

The crash was between a pickup truck and and an SUV, according to Ontario Provincial Police spokesperson Sgt. Mike Golding. The OPP said the crash happened north of where Highway 72 intersects with Highway 664 at about 9 p.m. CT time Saturday.

That's about 10 kilometres south of Sioux Lookout, the OPP said.

ROAD CLOSURE: Hwy 72 near Cedar Point Dr, 10 km south of <a href="https://twitter.com/hashtag/SiouxLookout?src=hash&ref_src=twsrc%5Etfw">#SiouxLookout</a>: Hwy closed due to collision. ^kw —@OPP_COMM_NWR

"The driver of the SUV had to be extracated [from the vehicle] and appears to have some serious injuries," Golding said. "Both drivers of both vehicles were flown to Thunder Bay for medical evaluation."

"I do believe they both have serious injuries."

In a written release issued Sunday afternoon, police said those injuries were not considered life-threatening. Three other people in the pickup truck also required medical attention, police said.

The OPP said the highway reopened around 10 a.m. CT Sunday.

Traffic collision investigators were on-scene during the closure probing what happened and collecting information, such as the condition of the road, as well as taking photographs and analyzing skid marks, Golding said.

OPP were still investigating the crash Sunday afternoon, police said, adding that the cause of the crash was still unknown.