The cycleway on the northern side of the Dublin Street Bridge is closed for maintenance work and a pipe inspection.
Wayne Armishaw, of GasNet, said it was also unsafe for cyclists to use the walkway on this side of the bridge while they were undertaking the work - and instead should use the underpass beneath the south side of the bridge.
"We are checking all the pipes and doing basic maintenance while we're there," he said.
"At this stage, I can say the work will continue into next week but we're not sure exactly how long it will take."
Cyclists are still able to use the underpass beneath the south side of the bridge to travel in both directions, and the upper walkway on the northern side will remain open to pedestrians while the work is underway.