Health authorities say there is a risk of a diarrhoea and vomiting outbreak across Auckland as people come into contact with sewage-contaminated floodwater.

Te Whatu Ora Health New Zealand medical officer of health Dr Jay Harrower said public health agencies hadn’t seen an uptick in sickness yet, but an increase in gastroenteritis was possible.

“[Gastronetiritis] can be serious for those who are very young, very old, or, have underlying medical conditions,” Harrower said.

“If you develop symptoms that could be gastroenteritis and need health advice, contact your doctor or call Healthline for free anytime.”

“Floodwater can often be contaminated with sewage, farm runoff and other hazardous materials,” Harrower said.

“If you have contact with flood water, flooded property or items contaminated with flood water you should wash your hands with soap and water and dry them thoroughly afterwards.”

Volunteers and staff help with the clean-up after a Campbells Bay restaurant was flooded after the record rainfall in Auckland. Photo / Brett Phibbs

The Auckland Emergency Management (AEM) group said the water can also contaminate flood-stricken houses, creating a risk people could get sick from cleaning and clearing the damage.

“It is important to clean and dry your house and everything in it. Wear protective clothing,” AEM said.

Harrower said any increase in public health notifications of gastroenteritis in the “immediate short-term” was likely to be small because there is limited testing for the illness.

“People’s stool samples are only tested if they seek medical care and have acute symptoms or if they are linked to a cluster of other cases.”

Stacy Gregg's home after heavy rains caused widespread flooding across the Auckland Region. Photo / Stacey Gregg

He also said the delay between the initial infection and feeling any symptoms could keep the number of official notifications low for now.

“While there is a risk of an increase in gastroenteritis across Auckland following the flooding, this has not been recorded in notifications to public health so far.”

Most people can treat themselves and “self-manage” gastroenteritis at home, Harrower said.

People should drink plenty of water if they fell ill, Harrower said, and antibiotics can treat severe gastroenteritis caused by bacteria.

John Mailata Clover Park's residence has been left devastated after the Auckland floods. Photo / Hayden Woodward

“To reduce the risk of passing on gastroenteritis to others you should regularly wash your hands with soapy water and dry them thoroughly, especially after using the bathroom and before preparing or eating food.”

While AEM said it was important to clean flood-damaged homes and record any devastation for insurance claims, people should keep safe while doing so and could find more information on the Auckland Council website.

People should not eat vegetables from gardens which have been flooded, due to the potential contamination. Lime can be sprinkled to decontaminate the soil.

There are nine sites around Auckland that people can access free of charge to dump flood-related waste.