SEATTLE — Alaska Airlines said flights were running close to normal late Monday after a fiber-optic outage shut down its ticketing system for more than four hours, causing the airline and its regional carrier to cancel 78 flights, affecting nearly 7,000 customers.

More than 130 other flights departed during the disruption, but some were delayed for as long as four hours, the airline said.

“Flights are running real close to schedule right now in all major cities. We expect tomorrow to be back on track completely,” airline spokeswoman Marianne Lindsey said Monday evening.

The problems started shortly before 8 a.m. when computers the airline uses to check in passengers went down, forcing employees to board travelers manually — in some instances sticking handwritten flight numbers to computer monitors.

The problems were caused by two severed fiber-optic lines in Sprint’s network.

Most affected were Alaska’s hub cities of Seattle, Portland, Ore., Los Angeles, Anchorage and the San Francisco area, Lindsey said.

Alaska Airlines and its regional partner carriers fly to 95 cities. Spokeswoman Bobbie Egan said it wasn’t immediately possible to say how many were affected. 

The 78 cancellations represent roughly 10 percent of 761 daily flights, she said.

At Seattle-Tacoma International Airport, frustration grew along with the lines of passengers waiting to check in, though some travelers simply sat or lay down and waited. Lines stretched out the door earlier Monday in the Alaska Airlines part of the terminal.

Airline representatives apologized and said technicians were working as fast as possible to restore the connection to the company’s Sabre reservation system.

No other airlines at Sea-Tac were affected by the problem, airport spokesman Perry Cooper said.

Passengers who had their travel disrupted were told they could quickly rebook without a change fee.

The problem was caused by a combination of two cut cables in Sprint’s fiber-optic network. One occurred at a construction site along railroad tracks between Chicago and Milwaukee and the other was somewhere between Portland and Seattle, said Sprint spokeswoman Crystal Davis in Reston, Va.

“Typically if there’s just one cut, traffic reroutes automatically,” Davis said. “Because there were two cuts within hours of each other, it caused this disruption.”

The Chicago-Milwaukee cable was cut accidentally due to some kind of work or maintenance, Davis said, adding she did not know who was doing the work.

The second cut involved an aerial cable that runs along power lines. It wasn’t clear late Monday how that got cut, Davis said.

Seattle-based Alaska Airlines is the seventh-largest U.S. airline based on passenger traffic and is the dominant U.S. West Coast air carrier, according to its website.

Alaska Airlines and Horizon Air are owned by the Alaska Air Group.