Transportation officials were forced to close a section of Highway 640 Thursday morning after a roadway collapsed, and it will remain closed until next week.

Hydro Quebec crews were digging a tunnel for a conduit near Claude Leveillée Ave. when they noticed part of the nearby road began to sink.

The crews noticed around 5:30 p.m. Wednesday that the roadway had sunk six centimetres and they became quite concerned.

As a result, Highway 640 West was closed from Claude Leveillée to Route 335, creating a kilometres-long traffic jam on the highway. That also created a lengthy delay on Highway 25 south as drivers tried to avoid the closed highway.

"This highway has asphalt and then concrete underneath so it would have stayed but at the moment we have a doubt. We cannot allow it to go further, so with no risk to take for the safety of the people so we decided to settle the problem right away," said Francis Labbé of Hydro Quebec.

"We're working on a solution, a permanent solution."

Inspectors from the Ministry of Transportation were at the work site Thursday morning as they tried to determine exactly what had caused the collapse and the best way to fix it.

The road was built over a swamp and the ground is very wet. At this point crews believe some other section of terrain had eroded, creating an air pocket that sagged once crews began digging the tunnel.

“We presume there's an air pocket and we don't know which size,” said Labbé. “We're going to dig at the lower end and we're going to fill this up and we're going to put a temporary pavement on.”

Transport Quebec soon realized that repairing the highway would take days, and would likely not be done until after Christmas.

Over the next 24 hours Hydro Quebec crews will fill the hole and ensure that nothing else is going to sag.

At the same time Ministry of Transportation workers will likely set up a counterflow lane on the eastbound side of the highway so that drivers can travel in each direction instead of taking a lengthy detour.

The complete repaving will have to wait until spring.