Up to 70 homes and other buildings have been destroyed in a ferocious firestorm that ripped through a picturesque seaside town on the NSW far south coast and is still burning out of control.

The 1000-hectare blaze around Tathra, east of Bega, which started on Sunday afternoon was fanned by very strong winds and high temperatures in the state’s east.

Authorities began assessing the area at first light on Monday and say the destruction of homes is likely to rise.

“Our early indications are that the number of buildings impacted is likely to climb above 70, but we will confirm that with the work of the building impact assessment teams this morning,” RFS Commissioner Shane Fitzsimmons told Network Seven on Monday.

“It’s an awful situation throughout the community of Tathra, where we have damaged buildings, damaged homes, and infrastructure,” he said.

He described the blaze as a “firestorm”.

“It was raining fire embers through the township – there were spot fires starting all throughout the streets of the town,” he told 2GB Radio.

The blaze remains out of control after burning through several kilometres of bushland and crossing a river before reaching Tathra.

Hundreds of residents from the township of 3000 were forced to sleep in a Bega evacuation centre 20km inland, or in their cars.

Bega Valley mayor Kristy McBain said on Monday there was a “level of helplessness as residents wait for information on what the real impact (of the fire) will be”.

“No lives were lost, which is the best news possible,” Ms McBain said.

She says authorities are assessing damage to critical infrastructure including water, sewerage and roads.

After visiting the Bega evacuation centre at the Showground early on Monday, Ms McBain said “the community is already banding together”.

Communication has been hampered after mobile phone towers collapsed, with Tathra only receiving five per cent of mobile phone coverage on Monday.

Meanwhile, Premier Gladys Berejiklian says her government will do what it can to help affected residents.

She thanked firefighters for their efforts and plans to visit the area herself as soon as possible.

“So many homes lost and people displaced in quite a shocking way, I can imagine it is only beginning to sink in and the next few days will be tough.

“I want everybody to know that we will do everything we can to make it easier for them,” Ms Berejiklian told the Seven Network.

The Insurance Council of Australia has declared the fire a “catastrophe”, meaning claims by those affected by the blaze will be given priority.

While the threat level was downgraded late on Sunday night after a southerly wind change helped ease hot conditions, flare-ups on Monday remain a concern.

Mr Fitzsimmons says there’ll be no rest for fire crews.

More than 100 firefighters working with aircraft and bulldozers are “trying to gain the upper hand” on the fire, which “remains very active and needs to be contained and consolidated today”, he said.

“It’s still a very dynamic situation. There’s a lot of very active fire edge to the north of the fire ground.”

No-one has been reported missing so far.

“We did have one woman to the west of Tathra yesterday afternoon hospitalised with burn injuries and inhalation of hot air,” Mr Fitzsimmons said.

Tathra Public School, Bega High School, Tanja Public School and Bournda Environmental Education Centre were not damaged but will be closed on Monday.

More than 22 fires are burning across NSW.

By Julia Carlisle