A group of foreign workers living in a house in Motueka have had a narrow escape after a poorly-installed fireplace sparked a fire in the roof.

Foreigners living in an "old wooden" house in Motueka have narrowly avoided tragedy after a faulty fireplace caused their roof to go up in flames.

Nelson Fire and Emergency senior station officer Craig Davies said fire officers had counted 14 beds in the Motueka house and only one working, but poorly placed, smoke alarm.

It had initially appeared as though the house had no smoke alarms and although one was eventually located, fire officers felt it would have afforded little protection for the occupants due to its placement.

GEORGE HEARD/STUFF Eight fire crews from Nelson Tasman were called to the blaze at the 14-bed house in Motueka, which had only one working smoke alarm.

Eight crews were called to the blaze before 8pm on Monday night to find the roof ablaze.

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"I'm not too sure how many people were actually living in the house at the time and English wasn't their first language," Davies said.

"They were extremely lucky to get away with their lives ... it was an old wooden house that was loaded with a lot of people."

Davies said because the fire had broken out early in the evening, the occupants had seen the smoke and all managed to escape without injury.

If smoke alarms weren't positioned well, they were rendered useless, and there needed to smoke alarms on the ceiling of every sleeping area.

"It certainly could have been a major tragedy with multiple fatalities in Motueka last night," he said.

"If it had been another couple of hours and they'd all been asleep, we could have been looking at multiple fatalities."

The fire had broken out as the fireplace had been incorrectly installed and "caught on" to the ceiling space.

"Everybody was lucky to get away with their lives. Everybody needs smoke alarms in their house, and they need a smoke alarm in every bedroom, especially places that have got a lot of people living in them like that."

Occupants of houses also needed to have escape plans.

Crews from Motueka, Kaiteriteri, Upper Moutere, Mapua and Nelson had attended the fire, and it had been a "good save" in that the house was still standing.

The roof would need to be replaced, however, and there was a lean-to area next to the house that had also been severely damaged. Fire crews had also managed to save most of the contents in the house, but there had been some water damage.

It's understood the occupants were a mixture of nationalities.

Motueka volunteer chief fire officer Mike Riddell said language had been a barrier, but he thought the occupants may have been seasonal workers from various countries, including European and Asian nationalities.

It highlighted the need for landlords who rented to seasonal workers to check smoke alarms were well-placed and positioned on the ceiling in every bedroom space.