Police are searching for a man who escaped from Sydney's Long Bay jail this morning.

David Mellis, 50, was reported missing from a minimum security area within the complex shortly after 11:00am.

He was last seen wearing a high-visibility vest and prison greens and is known to frequent the Glebe area.

A search was launched when a head check detected his absence and police were notified.

Police have urged anyone who sees him or knows of his whereabouts to contact them.