Authorities had not determined Thursday what caused a rubbish fire under the Nimitz viaduct that damaged fiber-optic lines carrying phone, internet and cable TV service, causing widespread disruptions most of Thursday for T-Mobile, Spectrum and Hawaiian Telcom customers.

Hawaiian Telcom spokeswoman Ann Nishida Fry said service was disrupted for roughly 30 business and government customers, primarily in the area of Daniel K. Inouye International Airport and west of the airport.

As of 5 p.m., its technicians had “successfully rerouted traffic” to restore phone and internet service to all but three customers. “Meanwhile crews continue splicing the five 72-pair strands of damaged fiber. They will work through the night until all services have been restored,” the company said in a statement. “We thank our customers for their patience and understanding as we work to make these emergency

repairs as quickly as possible.”

The fire occurred shortly before 10:30 p.m. Wednesday, when 15 firefighters responded and extinguished the blaze just after 11 p.m.

Capt. David Jenkins, spokesman for the Honolulu Fire Department, said fire investigators were not called out to what at the time was considered a routine rubbish fire put out in half an hour. He said the impact on utility service was not known at the time.

“The size and scope of the impact wasn’t apparent at the time of the fire,” Jenkins said.

Over the years, he said, rubbish fires in the area have been associated with accumulated trash at homeless encampments.

He said the department’s report on the fire was incomplete, but more information from the firefighters who were on the scene might be available today once they return to work.

Spectrum spokesman Dennis Johnson said the company’s customers in the lower Kalihi area were affected. Service was completely restored by 4:30 p.m., the company said. “Our engineers have repaired the fiber-optic cables that were damaged by the fire. We restored our services as quickly as possible. We appreciate our customers’ patience as we worked to repair the fiber.”

HMSA tweeted Thursday that its network was down. “A fire in Mapunapuna is causing technical difficulties, so we’re having problems with some of our phone lines and our email. We apologize for the inconvenience and are doing all we can to resolve the issue,” HMSA reported.

T-Mobile customers reported widespread service disruptions and a company official tweeted Thursday morning that, “Service is impacted and teams on the ground are working to repair as fast as possible.”

The impact of the Wednesday night fire mirrored a Jan. 15, 2013, rubbish fire that also damaged fiber–optic cables under the viaduct, causing widespread telephone, internet and cable television outages.

In that incident, a homeless man was hospitalized with burns to his face and arms after a rubbish fire on Nimitz near Kilihau Street that was reported just before midnight and took 2-1/2 hours to extinguish.

The state Department of Transportation said it is working with the Honolulu Authority for Rapid Transportation on a plan to prevent such rubbish fires.

State officials said last month that a growing homeless encampment was posing health and safety risks to the campers themselves as well as the surrounding community.

DOT spokesman Tim Sakahara said Thursday that cleanup under the H-1 viaduct that began Oct. 23 should be completed by today, after which HART rail construction contractors will be able to store equipment there. HART will have security measures in place, including surveillance cameras, to deter trespassing and any illegal activity or entry.

A security fence around the area is nearly finished, Sakahara added. The area extends from where Nimitz meets the H-1 freeway to Moanalua Stream.

“We expect that area to be much better once in use and people will know not to go there,” he said.