A grass fire that set off a blaze at 4.50pm on Wednesday had property owners between Warialda and Delungra worried overnight.

The fire was briefly brought under control on Thursday morning and the Gwydir Highway was opened again to traffic, but it flared up again within hours causing the police to shut down traffic so that problem trees could be dealt with.

Stephen Carstens, Namoi-Gwydir Membership Services Officer of the NSW Rural Fire Service, said the fire had claimed 318 hectares by Thursday afternoon when the mop-up process began.

“We are still concerned and are expecting challenging weather conditions over the weekend,” Carstens said.

By 4.30pm, the six tankers and 60 firefighters at the scene at midday had been brought back to 5 tankers and 15 firefighters monitoring the fire.

A house was in danger on Wednesday. “Thankfully, we made sure that it was kept safe,” he said. “A couple of outbuildings may have been burnt.” There were also power outages in the district.

Mr Carstens said the exact cause of the fire is still being investigated but there are suspicions that it may have been caused by a welding accident.