At one point, police closed all lanes of the 401 near Milton, for a crash that involved three transport trucks.
Two of them caught on fire, while the third managed to move far enough away to avoid the inferno.
Of the drivers in the affected vehicles, one managed to emerge unhurt, while the second driver suffered burns which could be serious.
The truck that didn't catch fire, was believed to be hauling dangerous goods, but police couldn't elaborate on what that was.
The westbound lanes of the 401 reopened after a couple hours, while the eastbound side remained closed into the evening.
No word yet on what triggered the collision.