It happened at about 16:00 BST on Saturday - the blaze spread from one house to neighbouring properties in Ballyoran Park. It gutted one house and badly damaged two others.
No-one was injured, but two dogs died as the fire spread.
At this stage police have said they are not treating the fire as suspicious.
Fire station commander William Weir said five pumps were brought in to bring it under control.
"On arrival the first crews found two houses well alight and the fire spreading either side of them along a row of five terrace houses," he said.
"It quickly became apparent that there was an oil tank involved which had allowed its contents to ignite which spread to a second oil tank in the house next door which then further added fuel to quite a large fire.
"The fuel then followed through the gardens of the remaining houses in the street and set fire to a further six garden sheds and some fencing.
"It was quite a large fire and it took crews approximately 35 to 40 minutes of hard fire fighting to stop it spreading to the other properties and to bring it under control and extinguish it."
Mr Weir said an investigation by the fire service and police had concluded that the blaze had started accidentally.
"Basically what happened was that some rubbish in the garden which had been burnt earlier in the day and left unattended re-ignited and set fire to a fence and then compromised the oil tank allowing its contents to become involved in the fire and from then the fire grew in intensity," he added.

The away side had the first chance of note, but Joe Healy sent his long-range thunderbolt wide 12 minutes in before Andy Cook found the side netting from Liam Ridehalgh's cross at the other end.
Rovers were awarded a penalty three minutes after the break when Connor Jennings was brought down in the box but James Norwood failed to convert as former Brighton goalkeeper Mitch Walker denied him an opener.
Tranmere's pressure finally paid off as they broke the deadlock in the 68th minute when substitute Stockton found space at the far post and got his head on the end of Ridehalgh's free-kick to hand his side their third straight win.
Match report supplied by the Press Association.
Match ends, Tranmere Rovers 1, Dover Athletic 0.
Second Half ends, Tranmere Rovers 1, Dover Athletic 0.
Andy Mangan (Tranmere Rovers) is shown the yellow card.
Substitution, Tranmere Rovers. Adam Mekki replaces Connor Jennings.
Lee Vaughan (Tranmere Rovers) is shown the yellow card.
Liam Ridehalgh (Tranmere Rovers) is shown the yellow card.
Connor Jennings (Tranmere Rovers) is shown the yellow card.
Substitution, Dover Athletic. Ross Lafayette replaces Moses Emmanuel.
Goal!  Tranmere Rovers 1, Dover Athletic 0. Cole Stockton (Tranmere Rovers).
Aswad Thomas (Dover Athletic) is shown the yellow card.
Substitution, Dover Athletic. Sam Magri replaces James Hurst.
Substitution, Dover Athletic. Aswad Thomas replaces Loui Fazackerley.
Substitution, Tranmere Rovers. Andy Mangan replaces James Norwood.
Substitution, Tranmere Rovers. Cole Stockton replaces Andy Cook.
Second Half begins Tranmere Rovers 0, Dover Athletic 0.
First Half ends, Tranmere Rovers 0, Dover Athletic 0.
Andy Cook (Tranmere Rovers) is shown the yellow card.
James Hurst (Dover Athletic) is shown the yellow card.
Joe Healy (Dover Athletic) is shown the yellow card.
First Half begins.
Lineups are announced and players are warming up.
A number of homes and gardens have been damaged in a fire in Portadown, County Armagh, after an oil tank caught alight.
[NEXT_CONCEPT]
Cole Stockton's second-half header proved enough as Tranmere beat Dover at Prenton Park to move level on points with National League leaders Lincoln.