A 20 hectare scrub fire is burning in swampland off Island Block Road, Waikato this afternoon.

Fire and Emergency New Zealand was alerted to the fire around 1.15pm.

Incident Commander Shane Bromley says four fire trucks, five tankers and two helicopters are responding to the fire, with another helicopter on its way.

"The fire is semi-contained but not controlled and we’ve put fire trucks in place to protect three houses as a precaution," Shane Bromley says.

"We are also working to protect the nearby Whangamarino Wetland and expect to have a crew at the fire ground overnight."

There will be another update at 7pm tonight.

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