Windows were blown out and roofs were lifted after a "freak" tornado in Greymouth overnight.

No injuries have been reported from the tornado, authorities say.

Local fire chief Kirk Gillan said it was "quite lucky" the tornado only affected back sections of some properties. One structure had lost over half of its roof, he said.

"One of them witnessed it coming, and he explained... he ended up hitting the floor and his window blew into bits and pieces. They reckon it was pretty scary," he said.

"But there was another occupant who lost their garage, was sleeping metres away, and didn't hear a thing."

Grey District Mayor Tania Gibson said four houses were affected by the "freak incident," along with one school. She said building inspectors had been deployed to the buildings.

The mayor said one man had to move out of a damaged house, but that other residents were in the process of boarding up windows and repairing damage.

"They do happen every now and then, and they seem to bounce over and affect the direct line they take," she told 1News. "Everything is under control and our emergency services have everything sorted — getting all the resources in they need."

Gibson told residents to get in touch with the council if they needed any help.

Meanwhile a few trampolines had gone missing from properties overnight, Gillan said.

Cobden School principal Noula Markham said that there had been "minor damage" to one of its buildings. Photos sent to 1News show some of the damage to the school's roofing.

"We had an extremely lucky escape with minor damage to our pool roof," Markham said.

Earlier, Fire and Emergency said it was called to Fox St, Cobden, at about 12.50am with firefighters sent to two houses. A police spokesperson said a resident in the street had called to say windows had been blown in by what appeared to be a tornado.

"While they were on the phone with police, the person reported their neighbour's roof had come off."