CONCORD, N.H. — Transportation officials say they won’t know until this weekend whether repairs to a bridge that links New Hampshire and Maine will be enough to reopen the Piscataqua River’s vital shipping lanes.

The center span of the 73-year-old Sarah Mildred Long Bridge got stuck Wednesday during a routine test.

Repair crews have been working on the bridge from sunrise to sunset, in what Bill Jannelle, New Hampshire Department of Transportation operations director, described as “brutal” weather conditions.

“It’s not just the temperature, it’s the wind whipping up and down the bridge and the river,” Jannelle said. “We’ve got a crew out there that knows that bridge and they’re doing a great job.”

Jannelle said it appears an electrical malfunction prompted one of the lift motors to keep running, which knocked the lift mechanism out of alignment. Repairs should be completed sometime Saturday, Jannelle said, but officials won’t know if the lift mechanism is fully repaired until they try to raise the bridge.

Portsmouth Harbormaster Tracy Shattuck has a crew on a 30-foot safety boat beneath the bridge in the event of an emergency.

“If someone falls off the construction crew, we’ll be able to pick them out of the water and thaw them out,” Shattuck said.

Up until Friday, lobster shipments and a barge carrying biodiesel were delayed. But Coast Guard Lt. Nick Barrow said three deep-draft cargo ships were scheduled to arrive at terminals along the river between Friday and Monday, including one with heating oil bound for the Sprague Energy terminal in Portsmouth.

Grant Brown, vice president for investor relations and marketing at Sprague, said they expect no supply disruptions if the bridge reopens Saturday.

“If it stays down, it will cause more challenges,” said Brown, who said the ship would be rerouted to their terminal in Quincy, Mass.

Another cargo ship is slated to arrive at National Gypsum on Monday, and public relations director Nancy Spurlock it will be rerouted to another of their plants if the bridge remains down. The third ship is carrying coal and is scheduled to arrive at Public Service of New Hampshire’s Schiller Station power plant Sunday.

“The shipping up and down that river is critically important to New Hampshire’s economy,” Jannelle said. “Our priority is to get that shipping traffic moving again.”

Shattuck said few people outside the area understand the ripple effect on the local economy of the cargo ships pulling into port.

“When a ship comes in the pizza guy is making money, the taxi driver’s making money,” Shattuck said. “Everybody’s really being affected.”

Drivers have also faced delays. With the Memorial Bridge still under construction, the disabled bridge left the Interstate 95 bridge as the only span linking Portsmouth, N.H., and Kittery, Maine.

Jannelle has dealt with at least three calamities at the Sarah Long bridge in the past year, including a lightning strike.

“It’s becoming more and more deteriorated,” Jannelle said. “There seem to be more and more problems. We really need a new bridge.”