Health warnings have been issued at dozens of Auckland beaches because of concerns about wastewater overflow and poor water quality following today's torrential downpours.

An alert system on Auckland Council's Safeswim website warns of wastewater overflow at all of the central beaches and says swimming is "not advised".

The warning was in place for Mission Bay Beach, Browns Bay, Castor Bay, Herne Bay, Mairangi Bay, Narrow Neck, Okahu Bay, Point England and St Mary's Bay.

Warnings at other beached involve elevated health risks because of poor water quality.

More than 50 beaches are affected in total, ranging in location from Wenderholm Beach to Kawakawa Bay.