Transport across Auckland has been affected by today's heavy rain, with congestion after flooding closing a number of roads.

The region is under a State of Emergency.

Waka Kotahi Auckland Regional Manager Jacqui Hori-Hault says it could be a long commute.

"To those who do still need to travel tonight, we are warning that the traffic will be heavy across the network for some time, so we're just asking people to be patient, careful and considerate toward other road users."

Auckland's under a heavy rain warning until midnight - and there are severe thunderstorm warnings in place for Western Bay of Plenty, Tauranga, Whakatane and Rotorua.

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