An extensive sea and air search far off the Queensland coast has been suspended with one man still missing after a boat capsized four days ago.

Two other men were rescued after their vessel got into trouble about 180 kilometres off Mackay on Thursday night, but there has been no sign of the 41-year-old.

“It’s so far off [the coast], by the time we get planes and helicopters out there they have to turn around and come back, they can’t spend that much time,” police Inspector Andrew Godbold said on Monday.

“Using the information that we’ve got from our experts, we estimate probably a day and a half to two days is about the most you could stay alive out there.”

The outcome was heartbreaking for the family of the missing man, Insp Godbold said.

“They’ve lost one of their sons, it’s just a terrible time for them,” he said.

“While we hold serious concerns for the man’s welfare, I ask the boating community to be vigilant and to report sightings or information to police immediately.”

The boat capsized on Thursday night and two other fishermen were rescued on Friday. One of them is the missing man’s brother.

They sent out an emergency alert from Creal Reef on Thursday night.

It took police boats between five and six hours to reach the area but visibility was poor.

A rescue helicopter spotted a man clinging to the hull of an overturned vessel on Thursday night before losing sight of him.

“Once they got in closer, for some unknown reason, the man has become detached from the vessel,” Senior Constable Syrrell Howard said on Friday.

On Friday morning, a plane spotted one man and he was rescued and airlifted to Mackay Base Hospital.

The second man was rescued just over five hours later and also taken to hospital.

– AAP