The Fire Service has dealt with two blazes in the South Island.

One was in Invercargill, in a cluster of flats in Tweed Street just after midnight.

Spokesman Andrew Norris says there were fears someone might be inside, however a search confirmed the property was empty.

The fire is being treated as suspicious and police have maintained a watch on the property overnight, he said.

Meanwhile in Ashburton, part of the roof of a house had to be removed so crews could put out a fire at an empty property.

Three trucks attended, and the fire is not being treated as suspicious.