A fire at a popular restaurant in Hamilton has left a black hole on the main street.

The Domaine was ablaze when firefighters arrived at Victoria Street at 2:30 this morning.

NZME reporter Belinda Feek arrived not long after.

She said 60 firefighters were on scene at the fire's peak, with crews swapping out as they got too hot and fatigued from fighting the blaze.

"On my way into the city this morning smoke could be seen billowing right across the city. Arriving at the scene there were flames bursting out through the top of the building."

Domaine building owners Brian and Raewyn Milicich, who live in an apartment above an adjacent building, were standing wrapped in blankets on the footpath still in shock about what happened.

Mrs Milicich said they were alerted by the noise of the firefighters outside.

"Brian said it will be the [street] cleaners but when I opened the door we could smell the smoke."

The couple quickly grabbed some clothes as the smoke poured inside before making their way out.

The couple have owned the building and the attached apartment since about 1998.

Jane Hailwood, co-owner of Azzurra Fashions, arrived at the scene about 6am to find her shop flooded, which she said was due to a burst water main.

Mrs Hailwood said they would have to wait for insurance assessors to get into the shop before knowing how much damage had been caused.