A smoky fire broke out Sunday on the westbound Chesapeake Bay Bridge, backing up cars for miles as motorists returned from events in Delaware and Ocean City, Md.

The fire began about 6 p.m. near the bridge’s highest point, just beneath the roadway in material being used to paint the structure, authorities said.

No injuries were reported, and the shutdown lasted for about two hours, said 1st Sgt. Jonathan Green of the Maryland Transportation Authority Police.

The fire apparently started in a tarpaulin spread over the network of support girders under the concrete roadway, said Assistant Chief Paul Schlotterbeck of the Kent Island Volunteer Fire Department. It was not immediately clear what caused it.

Two towers support the suspension portion of the bridge, and the blaze broke out near the eastern tower, where the deck is about 180 feet above water. Firefighters climbed down from the deck to reach the blaze, Schlotterbeck said. “Our guys will do whatever it takes,” he said.

Cars were turned around, and the eastbound span went into two-way operation. A NASCAR race in Dover, Del., and a wine festival in Ocean City likely added to the traffic.