Thousands are expected to converge on Sydney's first metro line on Sunday after the state government decided to make the opening day free for passengers.

The 13 stations on the $7.3 billion Northwest Metro line between Rouse Hill and Chatswood will be opened to the public just after 11am on Sunday. The last metro train will leave Chatswood at 10.05pm and, from the other end of the line, from Tallawong station at Rouse Hill at 9.35pm.

A driverless metro train at the new Tallawong station in Sydney's north-west.

Given anticipated interest in the long-awaited opening, NSW Transport Minister Andrew Constance urged people to stagger times during the day on which they decided to ride on the new line.

"Trainspotters will become train riders on Sunday. If you can come later in the day, that would be preferable because there will be large crowds," he said.