Commuters face the prospect of the shutdown of Sydney's Epping to Chatswood rail line extending into an eighth month if contractors find they need more time to convert the railway to carry single-deck metro trains.

The 13-kilometre heavy rail line is due to be closed on September 30 for a seven-month period, forcing up to 20,000 commuters a day to catch replacement buses or drive.

The Epping to Chatswood line will be closed on September 30. Credit:Jon Reid

But leaked documents, obtained by the Herald, show transport officials expect the $8.3 billion metro line from Rouse Hill to Chatswood to be opened to passenger services “no earlier than” May 5 next year.

And sources say there are contingency plans for the Epping to Chatswood line to be closed for an eighth month if more time is required to convert it to metro standards.