An urgent search is underway for a potentially armed man missing for almost a week in rural north Queensland.

Marcus Bismark, 44, was last seen walking along Gregory Developmental Rd, about 250km west of Townsville, about 1.30pm on Saturday after his vehicle broke down.

He has not been seen or heard from since.

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Police and family hold serious concerns for Bismark’s welfare due to a medical condition and the length of time he has been missing.

Officers also believe he may be in possession of a firearm and have warned members of the public not to approach him if he is spotted.

Instead, anyone who sees Bismark is urged to immediately contact police.

Marcus Bismark was last seen on Saturday. Credit: Google Maps, Queensland Police

Bismark is described as about 180cm tall, with a solid build, dark complexion and black hair.

He was last seen wearing long black pants and no shirt.

Police have appealed directly to Bismark to make contact and let authorities know he is safe.

Anyone with information about his whereabouts is also urged to come forward.

Officers are also seeking dashcam footage that may have captured Bismark in the Greenvale region on Saturday.