After an hours-long shutdown this morning all of Highway 400's southbound lanes have re-opened to traffic, though a backlog created by the closure is likely to cause significant delays for drivers.

The traffic headache began just after 5 a.m. Thursday when police say a dump truck travelling south on Highway 400 with its bucket partially raised smashed into a large overhead highway sign near King Road. All southbound lanes of Highway 400 were closed as crews worked to remove the sign, which was bent in the collision and hung precariously over the highway.

"Crews got on the scene and looked at the structure," OPP Sgt. Schmidt told CBC News. "They assessed it and found it to be unsafe for people underneath the bridge. It would cause considerable damage if it was to come down completely."

Police say the truck that struck the sign had left the scene. They are asking for witnesses or anyone with information to contact the OPP.

The southbound lanes re-opened to traffic just after 10:15 a.m.

The closure, which hit during the height of the morning commute, created long delays as southbound drivers were diverted off the 400 and had to use alternate routes, including Weston Road and Jane Street, to get into the city. And although traffic is moving through the area again, drivers are likely to face delays on Highway 400 and its alternate routes throughout the morning.

Follow @CBCToronto and listen to 99.1 for the latest updates