Severe thunderstorms and flash flooding are forecast for much of the North Island today.

MetService has warned the storms may develop his afternoon and evening, from Waikato to Wairarapa.

"These storms are expected to be slow-moving and capable of producing flooding rainfall - 25-40 millimetres an hour," the MetService warning says.

"Rainfall of this intensity can cause surface and/or flash flooding, especially about low-lying areas such as streams, rivers or narrow valleys, and may also lead to slips."

People should take shelter immediately should severe weather approach or if they felt threatened.

The warning applies to Waikato, Waitomo, Taumarunui, Taupo, Hawke's Bay, Taranaki, Taihape, Wanganui, Manawatu, Tararua, and Wairarapa.

SOUTH ON WATCH

Meanwhile as Canterbury swelters through scorching temperatures today, locals are being warned to prepare for strong winds on Sunday.

MetService has issued a severe weather watch predicting a period of strong north-west gales for inland Canterbury on Sunday.

There was a chance of some severe gale gusts, especially about the foothills.

Heavy rain has been forecast for the west of the island.

A front over the Tasman Sea will move northwards across the South Island on Sunday with the MetService saying it should bring heavy rainfalls to the West Coast, causing spillover into the headwaters of Canterbury's lakes and rivers.

"It is likely that some or all of these areas will be included in a heavy rain warning closer to the event,'' it said.

- © Fairfax NZ News