Firefighters have contained a bushfire that may have been deliberately lit on the NSW mid-north coast.

The blaze broke out around 1pm (AEDT) on Friday in the Booti Booti National Park near Forster, forcing the closure of roads in the area and isolating the town of Green Point.

The NSW Rural Fire Service (RFS) said on Saturday crews were strengthening containment lines around the blaze as small areas of bush continued to burn.

The Lakes Way and Green Point Drive were now open to traffic as firefighters worked on the roadside, the RFS said on its website on Saturday.

Police said in a statement that they were treating the fire as suspicious.

They said Green Point residents who had left because of the fire have returned to their homes.

Meanwhile, three teenagers have been charged with deliberately lighting bushfires over the past two days in Newcastle.

Police said they charged the boys, aged 15, 16 and 17, with lighting bushfires on Thursday and Friday near the John Hunter Hospital.

All the blazes were quickly extinguished by fire crews, police said in a statement.

The 15- and 16-year-old boys were granted bail and will face Broadmeadow Children's Court on February 5.

The 17-year-old boy was refused bail and was due to face Parramatta Children's Court on Saturday.