Health warning remains in place across parts of the Banks Peninsula and Christchurch coastline after extremely high levels of paralytic shellfish toxins were detected in water samples at Port Levy.

Authorities are continuing to warn the public not to collect or eat shellfish along the northern side of Banks Peninsula, from New Brighton to Hickory Bay.

The warning follows testing which identified a toxin producing algal bloom.

Officials said the bloom poses a risk to both people and animals.

People have also been advised to keep away from the water in the Port Levy area and to exercise caution in nearby bays in case the toxin has spread.

Health officials said exposure to contaminated water may cause skin rashes, nausea, stomach cramps, and tingling or numbness around the mouth and fingertips.

“People should avoid contact with the water until further notice,” National Public Health Service Public Health Medicine Specialist Dr Imogen Evans said.

“If you experience symptoms such as skin irritation, nausea, stomach cramps, tingling or numbness around the mouth and fingertips, seek medical advice and let your doctor know if you have had contact with the water.”

New Zealand Food Safety has also warned people not to collect or eat shellfish anywhere along the northern side of Banks Peninsula between New Brighton and Hickory Bay.

Environment Canterbury said it continued to monitor conditions.

A spokesperson said paralytic shellfish toxins can accumulate in shellfish and pose a serious health risk if consumed.

“People should not collect or eat shellfish from affected areas until testing confirms it is safe again,” the spokesperson said.

Authorities said regular testing would continue and the warning would remain in place until toxin levels drop to safe limits.