Up to 30 homes have been destroyed or "seriously damaged" in bushfires burning in northern NSW.

Yesterday, the RFS issued emergency warnings for four separate blazes burning within about 100km of each other in the state's north.

While the immediate threat from those fires has eased, two of them joined overnight.

Those blazes at Drake and Busbys Flat have so far burnt more than 90,000 hectares of land.

"So there's an enormous amount of fire in that area," Deputy Commissioner Rogers said.

The RFS is not aware of any fatalities, and some residents have told the ABC they hid in sheds as the fire swept through.

The village of Rappville, south of Casino, is among the worst affected areas.

Vision from the fireground yesterday showed several homes engulfed in flames.

About 50 people sheltered in the local school last night.

Strong winds and soaring temperatures hampered firefighters' efforts yesterday, however, conditions have since improved.

"We've got teams on the ground this morning trying to assess that and sometimes they're sheds when we thought they might have been homes," Deputy Commissioner Rogers said.

"So we have to go through that and it does take time but it has to happen to make sure we give accurate news to those residents."

Prime Minister Scott Morrison said his thoughts were with those who had lost their homes.

"Fortunately there's been no loss of life which is something always to be thankful for, but there are remaining very serious threats today," Mr Morrison said.

"For those communities around Casino, it's going to be a very tough day but know that Australians are with you."

Yesterday, emergency warnings were issued for the fires at Drake and Busbys Flat, as well as blazes at Tenterfield and Jackadgery.

Deputy Commissioner Rogers said the RFS was "concerned" there had also been property damage at the Drake fire, which had been burning for weeks but flared up yesterday.