The official cause of a spectacular fire at the Port of Tauranga on Friday remains unknown, for now.

But the man investigating the fire says he thinks he knows what might have happened.

Bay of Plenty specialist fire investigator Luke Burgess was trawling through the scene of the fire near the entrance to the port yesterday , working to establish how the fire started.

"I've got a fairly good idea at the moment so I'm just trying to prove it ... trying to pinpoint the exact cause," he said.

Port chief executive Mark Cairns told the Bay of Plenty Times on Friday he believed an electrical fault was to blame.

Burgess said he expected to determine the exact cause of the fire in a couple of days' time.

Just after 11.30am on Friday, firefighters were called to a building fire at the port's Sulphur Point entrance.

A large fireball had engulfed an electrical and mechanical workshop and adjoining office building.

Three vehicles parked nearby were also damaged.

It's understood the port's insurance assessors will arrive today.

"The main thing is that all the staff got out safely," Burgess said.

"They followed procedure and they are in a process of recovery now.

"This is a really good example for businesses of why you should have an evacuation procedure."

Burgess described the fire as "a significant event".

Businesses are required to have a registered evacuation scenario reported to Fire and Emergency New Zealand every six months.