WATCH: Traffic disrupted as truck burns on N1 highway in Pretoria

Smoke billowed on the N1 north highway in Pretoria on Friday afternoon after a truck caught fire just before the Garsfontein off-ramp.

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Senior superintendent for the Tshwane Metro Police Department spokesperson Senior Superintendent Isaac Mahamba said a bakkie heading north on the N1 caught fire. The cause of the accident was still unknown.

Mahamba said there was a driver and two passengers "unaccounted for".

"The info we have is that there were two passengers and a driver, and their whereabouts are currently unknown."

Two lanes were closed on the N1 heading north before Garsfontein road while the vehicle was still ablaze and motorists were advised to use alternative transport.

According to Netcare911 spokesperson Shawn Herbst, the small truck was transporting oil.

The driver reportedly lost control of the vehicle, resulting in a collision and subsequent fire, Herbst said in a statement.

Hours have passed and the three adult male occupants who allegedly left prior to the arrival of emergency services are still not accounted for.

"The three occupants are still not accounted for and we do not know their whereabouts at this stage," Mahamba told News24 later on Friday afternoon.

The Fire and Rescue Services doused the fire and traffic on the N1 and the accident scene on the road has since been cleared.