Emergency services were called to Highcliff Rd shortly before 7pm following reports the 53-year-old cyclist was seriously injured.
The Otago Regional Rescue Helicopter took the man to Dunedin Hospital, where he was in a serious condition last night.
Fellow cyclist Nick Baker told the Otago Daily Times the man was part their group of four cyclists who were riding down Highcliff Rd.
"He was ahead of us ... we realised something was wrong when we got to Portobello and he was missing."
The group then doubled back and found the cyclist semi-conscious down a 6m high bank.
It appeared he failed to take a sharp downward bend, before riding through a wire fence, Mr Baker said.
Senior Firefighter Bill Dickson warned the area - known to locals as the "Seven Devils" - was a potential death trap for cyclists, with several injured this year alone.
"Someone will be taken away in a box from here."
A neighbour, who declined to be named, said he had taken three cyclists to hospital this year.
The narrow road, coupled with tight bends and steep slope made it a constant threat to cyclists and motorists alike.
"And don't get me started about campervans," he said.
