Shoalhaven Rural Fire Service district manager, Superintendent Mark Williams said while the actual cause of the blaze, which broke out in dense heathland around noon on Tuesday, January 26, is yet to be determined it is "suspicious".

"RFS fire investigators will be on the site this morning and will be working with Australian Federal Police to establish how the fire started," Supt. Williams said.

"Our crews are mobilising and will be investigating."

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He said the service was not aware of any lightning strikes in the area that might have started the blaze.

"It is a concern and I guess it also goes to show that even though we've had fire in that area in the past two seasons we can't sit on our laurels," Supt. Williams said.

"There are still a lot of unburnt areas, so we still have plenty left to do."

More than 30 RFS crews, including some from the Illawarra, battled the blaze, facing testing weather conditions, with temperatures in the high 30s and "shifting winds".

"We had winds from the nor west and also the prevailing coastal breeze which made for swirling conditions," he said.

"It made it tough for firefighters. We would prepare for wind from one direction and then be hit by wind from another.

"It was a flukey kind of wind and made it difficult, but all the crews did an outstanding job.

"They were under the pump and the backburning work they undertook in those conditions was amazing.

"All those containment lines held."

He said the fire was in a largely inaccessible area of heathland to the south west of the Jervis Bay airstrip.

"There are a number of trails in the area but once you get into the heathland it can be up to 12-15 feet high. It's often impregnable," Supt. Williams said.

"The only way to get through is to cut your way through using machinery and that's why we decided to burn at the side of the trails.

"The work the crews did in extremely hot and tough conditions was outstanding."

Crews were aided by three large air tankers which undertook a number of retardant dropping runs, three water-bombing helicopters and other fixed winged assets.

"We used the air tankers for six retardant tuns to the northern flank of the fire, which we knew would be a high pressure area when the southerly was due to hit later in the evening," Supt. Williams said.

"We extended the JB airfield area out to Caves Beach Road with retardant as a control line and that held firm."

Crews were able to contain the fire by 7.30pm, before the impact of the southerly change was starting to be felt at 8pm.

Supt. Williams said the change also brought with it some moisture, which was most welcome and assisted crews in their efforts.

The blaze was downgraded to advice level at around 9.30pm.

At the height of the emergency on Tuesday, Booderee National Park was closed and remains closed to the public today (Wednesday).

While there were no "official evacuations" tourists camping in the area were advised to leave, while the villages of Wreck Bay and Jervis Bay were put on alert, with residents told to monitor condition and be prepared to follow their Bushfire Survival Plans

Seven RFS crews remain in the area today.

Booderee National Park remains closed to the public, with crews continuing to undertake the "blackening out" process, monitoring the area and identifying any "dangerous trees".

"We will also have community engagement teams in the area, visiting both the Wreck Bay and Jervis Bay villages," Supt. Williams said.

"Our engagement teams will be filling residents in on what happened but will also be seeking any information into a possible cause of the blaze."

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