A large fire that broke out in the building of a plumbing company in Tauranga is being investigated.

The building on Birch Avenue in Judea, caught alight around 5.20 this morning.

It was previously thought the blaze was coming from the mixed martial arts fight club next door.

The fire was described as being well-involved, and 13 crews from around the region had to be brought in to help battle it. 

Fire investigator John Rewi said the fire started in a storage shed, which has extensive damage, while the fight club also suffered smoke damage.

The cause of the blaze is not yet known.