Three people got stranded on a Christchurch rooftop as a strong south-westerly blew through the city and knocked over powerlines on Tuesday.

Firefighters were called to a Ferry Rd property just before 1pm after the wind blew the powerlines onto scaffolding, leaving three people stranded on the roof, said a Fire and Emergency New Zealand spokesperson.

After the power was cut, the workers got down uninjured, they said.

It was one of six weather-related call-outs within about 45 minutes across the city.

The Press reported two trampolines — one in Aranui and the other in Burwood — were blown onto powerlines just after noon.

Windows were also blown out at the bottom of the gondola in the Port Hills.

A tree came down in the strong wind, blocking part of Yaldhurst Rd, while another was blown over at the corner of Curletts and Parkhouse Rds.

MetService said gusts at Christchurch Airport on Tuesday hit about 70km/h.

Ferry crossings cancelled

Several Cook Strait ferry crossings are being cancelled due to heavy swells on Tuesday.

A strong southerly wind is bringing large swells and gusts.

Interislander services between Picton and Wellington at 9.30am, 3.30pm and 9.30pm were cancelled on Tuesday, as well as the 3.30am on Wednesday 19 August.

"Safety is our priority and we only sail when it is safe to do so," said Interislander.

It said passengers would be contacted and rebooked to a different service.

Bluebridge has cancelled sailings between Wellington and Picton at 1.30pm.

"Due to limited re-booking options, standby lists across subsequent sailings will be operating from each port for affected customers to be added to," Bluebridge said.

Livestock transport firm Downlands Deer general manager Kris Orange said cancellations cost him time and money.

A mechanical fault on a ferry on Monday meant he had to rebook a truck for a Tuesday crossing, only to have all sailings cancelled.

"We had to unload the truck again and put all animals out into the paddock."

He said it caused extra stress for workers and animals.

-Allied Media and RNZ