A 70-year-old crocodile that survived Cyclone Tracy has again been tested against the elements — this time emerging unscathed from a fire that claimed the home of its owners.

Emergency crews were called to the property in Fannie Bay just after 10am on Thursday morning and were surprised to find four-metre-long Albert in a pen at the back of the property.

"We found an elevated residence full in flame," firefighter Bill Gleeson said.

A single male occupant of the granny flat escaped uninjured.

"We had residents outside, it was confirmed nobody was inside. That was great relief to crews," Mr Gleeson said.

The top floor of Helen Haritos's home was destroyed, but her pet Albert, who has been in the family since 1958, was safe in its enclosure.

"Thankfully the crocodile didn't affect our operations at all," Mr Gleeson said.

"[Albert] is well contained and completely unaffected by fire. He seemed quite happy to look at me as I was checking the premises."

The house was home to the Haritos family and a saltwater crocodile named Albert. ( ABC: Jano Gibson )

Crocodile ranger Tom Nichols was called in to determine whether the reptile needed to be relocated.

"This is definitely a first for me," said Mr Nichols, who usually pulls crocodiles out of traps around Darwin Harbour.

"I just mainly wanted to make sure the pen was secure and I could get in touch with the owner."

Albert is believed to be the only adult saltwater crocodile living in a backyard in suburban Darwin, and Mr Nichols said the family has a permit.

"This crocodile was in their possession since before crocodiles became a protected animals," he said.

Helen Haritos has previously spoken to the ABC about her affection for the reptile.

"It's not quite like my dog but I do have a particular bond and care for the animal," she said last year.

"It's quite easy actually [to look after]; I'd say low maintenance, but treat with respect because they are very dangerous animals."

Her father, croc hunter George Haritos, caught Albert in the Mary River in 1958, and Helen inherited the reptile in 1992 when he passed away.

The cause of the fire appeared to be an iron that had been left on, said Watch Commander Senior Station Officer Nick Bell.

"This serves as a timely reminder to check electrical appliances including irons and hair straighteners before leaving the house," he said.

He also reminded residents to check that smoke alarms were working and to replace their batteries every year.