Updated 1:36pm: The trial of a man charged with starting a devastating fire at a self-storage facility in Wellington is underway.

The man, who has interim name suppression, is facing a judge alone trial in the High Court in Wellington.

The fire he’s charged with lighting destroyed an entire floor of one block of Kiwi Self Storage in Kilbirnie in April.

Hundreds of people lost belongings in the blaze.

Crown prosecutor Sally Carter has outlined the evidence the crown will present during the trial - which she says is layers of circumstantial evidence.

"The most significant piece of evidence is that a cap that was worn by the offender was found at the scene."

Hundreds of customers' goods destroyed

The High Court in Wellington has heard of the distress caused by a fire at a self-storage unit in Kilbirnie.

A statement written by the General manager of Kiwi Self Storage Howard Trautvetter has been read aloud.

In it, he describes the reaction of the 220 customers, whose units were destroyed or damaged in the fire.

"Some found a few salvageable goods and many lost irreplaceable items such as photographs.

"The experience for these customers was very emotional and distressing.

"A lot burst into tears at the sight of their burnt goods."

The statement says customers are strongly encouraged to purchase insurance, but it's not mandatory.