Police have resumed the search for a man who is believed to have fallen into the Brisbane River and gone under.

Water police boats and divers returned to the river at first light on Monday morning, more than 36 hours after 34-year-old Matt Jarvis was reported missing.

Water police boats and divers returned to the Brisbane River on Monday to search for Matt Jarvis. Credit:Jocelyn Garcia

Friends say they saw Mr Jarvis' arm in the water before he went under and never resurfaced.

Acting Inspector Teena Rolls said Mr Jarvis was drinking with a group at the barbecue area at the bottom of the Kangaroo Point cliffs when he walked off towards the water's edge about 7.45pm on Saturday.