Aucklanders are being warned to remain alert for ongoing dangers, as this morning's heavy rain starts to ease.

Red and Orange Heavy Rain Warnings remain in effect for Auckland, Great Barrier Island, the Coromandel Peninsula, the Bay of Plenty, and the northern Gisborne District.

Auckland and Northland remain in a state of emergency, with emergency services receiving dozens of calls for assistance.

The Northern Motorway between Esmonde and Northcote has reopened following flooding, but Western train lines won't be running until further notice.

Auckland Emergency Management Duty Controller Rachel Kelleher says the situation has ramped up in the past few hours.

She says there is surface flooding, downed trees and road closures across the city, and people should avoid driving if they can.

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