An issue with communications halted all Sydney Metro trains on Monday morning, stranding commuters for up to an hour.

Shortly before 10am, the Transport Management Centre released a statement saying services "are not running in both directions between Chatswood and Tallawong due to a communications system issue".

The entire Metro line has been halted due to a "communications service issue". Credit:AAP

Replacement buses are being organised but are not yet on site, the statement said.

"Passengers are advised to delay travel, consider alternative travel options or allow plenty of extra travel time until the replacement buses start running.