Otorohanga resident are still assessing the devastation caused by last night's heavy downpours

A man died while travelling on State Highway 39 - when his car was submerged in floodwaters.

A state of emergency is in place for the week ahead - with Mayor Rodney Dow warning locals to stay home.

He says rainfall reached up to 300 millimetres within an hour - and it could take days to understand the impacts across the community.

The Otorohanga Museum was among the sites inundated - with knee high-flood waters soaking taonga, including the waka.

Creative Coordinator Rebecca Ngapo, says it's mind-blowing how much water came down.

She says there's a lot of work to do - bringing in dehumidifiers or fans, and checking the power.