A massive smoke cloud rising near Milton yesterday prompted queries about the possibility of an explosion.
But the cloud proved to be from a burn off.
Fire Service spokesman Andrew Norris said firefighters from the Milton Volunteer Fire Brigade were called just before 3.30pm to a large vegetation fire in the ''foothills'' near North Branch Rd.
The cloud of smoke was seen by people from Mosgiel to Milton.
Several contacted the Otago Daily Times asking if the smoke was the result of an explosion.
Mr Norris said the permitted fire created plenty of smoke and was ''under control'' when the firefighters arrived.
Otago Rural Fire Authority deputy principal rural fire officer Kerry O'Neill said the vegetation fire on a farm was started by squirting ''fire gel'' from a helicopter.
''It's a bit like napalm ... it comes down in little fire balls.''
When the gorse was set ablaze and the fire ''took hold'' a large smoke column stood tall on the calm day.
As the fire progressed, the smoke dispersed, he said.
Troy Latta said he was at a friend's house in Milton when he saw the smoke cloud rise.
He thought the ''big mushroom cloud'' was the result of a ''major bush fire''.
He went for a closer look and reached Table Hill Rd, which was ''smoked out''.
Firefighters were monitoring the fire from the area and told them it was a controlled burn of gorse, Mr Latta said.
'It is a much more efficient way of getting twice as many apples using a lot less water.'