ROCKWOOD, Ont. -- Two adults and a teenager were killed when a pickup truck collided with a car near Guelph, Ont., provincial police said, noting it was the second highway tragedy in southern Ontario in less than 24 hours.

"This is devastating and we're only partway through this long weekend," said Const. Cheri Rockefeller.

She said the crash involved a pickup truck and a sedan and occurred near the community of Rockwood, Ont., just east of Guelph, around 8:30 p.m. on Saturday.

Rockefeller said a passenger in the car, a 35-year-old man from Fergus, Ont., was pronounced dead on scene.

She said also in the sedan was a 17-year old male passenger and a 45-year-old female driver, both of whom are from Fergus, Ont., and that they were taken to hospital where they later died.

Rockefeller said the names of the victims will not be released until next of kin is notified. She also said investigators know the relationship between the occupants of the sedan but will not be immediately releasing that information.

"Nothing is being released in regards to that as of yet. We're still looking at confirmation," said Rockefeller.

She said the driver of the pick-up truck was a 50-year-old man from Barrie and that he was not injured in the crash.

Rockefeller said no charges have been laid and the cause of the collision is still being investigated.

At the start of the long weekend, Ontario Provincial Police warned that officers would be out in force looking for aggressive, distracted and impaired drivers, as well as seatbelt violators.

"We're hoping that drivers are going to refrain from risky behaviour and buckle up and get to where they need to go, and get home safely," said Rockefeller.

The other fatal collision that occurred over the long weekend was northeast of Toronto.

Provincial police reported early Saturday morning that an SUV crossed into oncoming traffic in Port Perry, Ont., and collided head-on with a car.

Three people in the car -- a 59-year-old man and two women aged 55 and 44 -- were killed, and a 41-year-old woman who was also in the vehicle suffered critical injuries.

The 68-year-old man driving the SUV was being treated for serious injuries.

Rockefeller said collisions are more likely to occur on weekends because there's usually an increase in traffic.

"I'm just hoping people pay attention on the roads and recognize the fact that we're are out there with heavy police presence, and that people abide by the rules of the road," she said.