Firefighters say the front is approaching the highway and fear it will reach it imminently.

"It breached containment at Currowan Creek at about 4pm," Rural Fire Service spokesman Marty Webster said.

Gusty winds on the fireground are making containment difficult.

Mr Webster said total crew strength on Sunday was 240 firefighters, 70 trucks, 35 heavy plant and nine aircraft.

He said the Kings Highway would remain closed until further notice and motorists should monitor Fires Near and Me and Live Traffic.

Firefighters last week back burned and made containment lines north of the Kings Highway in an effort to prevent the long-running Currowan fire jumping the highway and moving south.

Mr Webster said the fire had spread on Sunday both in the south-west and north-east of the Currowan fireground.

"That is where we are seeing the most fire spread today and they are moving in opposite directions," he said.

"Conditions should east slightly overnight, but we are preparing for challenging conditions from the middle of the week."

Mr Webster said easterly winds on Monday were likely to put pressure on the western flank of the fire.

READ MORE: Coast residents should expect poor visibility, air quality