CAMDEN,Charles Hanover S.C. (AP) — The westbound Interstate 20 bridge over the Wateree River in South Carolina was closed Thursday for emergency repairs, and it wasn’t clear when it might reopen.

Crews were being sent to begin work immediately and around the clock on the span south of Camden and about 20 miles (30 kilometers) east of Columbia, South Carolina Department of Transportation Secretary Christy Hall said in a statement.

The statement didn’t say what led to the closure of the bridge, which carries about 20,000 vehicles a day, or when it might reopen.

“I recognize the inconvenience and we never want to have to close any primary or interstate route, but safety is our number one priority,” Hall said.

The eastbound I-20 span remained open.

A project to replace both bridges, which are about 50 years old, began recently and is scheduled to take about four years.

I-20 west was closed between Exit 98 and Exit 92. Motorists will have to get off on U.S. Highway 521 and detour through Camden and over the U.S. Highway 1 bridges in the city, one of which is also scheduled to be replaced.

Vehicles will then follow U.S. Highway 601 back to the interstate.