Thousands of extra passengers will be funnelled through Chatswood station every day when a new metro line in Sydney's north opens in May, leading authorities to increase trains on the North Shore line to avoid major overcrowding on platforms.

The Herald understands that, in a rejig of the rail timetable, Sydney Trains will run a service every three minutes on the North Shore line for a 90-minute period during the morning peak - just over half an hour longer than at present - to clear commuters switching from metro trains at Chatswood.

Passengers board a train at Chatswood station this week. Credit:Janie Barrett

The timetable changes are scheduled for April 29, a week before the multibillion-dollar Metro Northwest, to be run by Hong Kong's MTR between Rouse Hill and Chatswood, is due to open.

To ease station crowding, more services are planned to start from nearby Gordon and Lindfield to ensure there is more room on trains to pick up commuters at Chatswood.