Police have rushed to a Darwin unit block rooftop after a report of a man with a rope tied around his waist who appeared to be preparing to jump - only to find he was attempting to enter his own residence through the balcony after he locked his keys inside.

Duty Superintendent Louise Jorgensen said police received a call yesterday evening just after 6:30pm of a "suspicious male on the roof of an apartment block" in Woods Street, Darwin city.

"From all appearances it looked as if he was counting the number of floors down and was preparing to jump," she said.

"Police attended and the male was pointed out to them. They rushed to the roof and found the male standing near the edge with a rope attached to a nearby pole."

She said police, fearing for the man's immediate safety, urged him to move away from the edge and enquired about his actions.

Supt Jorgensen said the man, in his mid 20s, told police he lived in the unit block and had locked his keys inside.

Superintendent Del Jones said the man did not want to pay for a locksmith.

"But obviously that's a far better option than having to rappel down the building to your apartment," she said.

Superintendent Jorgensen said the man "to his credit" had decided it was too dangerous and was preparing to pack his abseiling attempt in when police arrived.

"He agreed that having a spare key or utilising the services of a locksmith would be a better idea in the future should he unfortunately lock his keys inside again," she said.

"I think there is a lesson in this for all of us."