Heavy rain is pummelling parts of the country, causing widespread travel disruption, flooding and evacuations.

The top of the South Island is bearing the brunt of the rain, with state of emergencies issued as a result of significant rainfall. Dozens of homes have been evacuated due to rising floodwaters.

Fire and Emergency said it has responded to 31 calls, with crews rescuing people trapped in vehicles, assisting with evacuations and pumping water from flooded homes.

Meanwhile, Auckland has been hit by severe thunderstorms and torrential rain.

Here's what you need to know.

A state of emergency has been declared for the Nelson Tasman region as a result of severe weather and evacuations.

Tasman District Council said the declaration will allow agencies to rapidly respond, with slips and flooding across the region and further rain forecast.

People are being evacuated in Brightwater and Upper Moutere and residents in Riwaka might need to leave.

A local state of emergency is also in place for part of Marlborough, where 60 households in Spring Creek near Blenheim were ordered to evacuate because of fears a Wairau River stopbank might not hold.

Fire and Emergency (FENZ) has activated its Local Coordination Centre in Nelson to coordinate its response activities across the whole top of the South area.

Bronwyn Webby has been evacuated from her property in Lower Moutere because her home is surrounded by rapidly rising floodwater.

Bronwyn Webby has been evacuated from her property in Lower Moutere because her home is surrounded by rapidly rising floodwater. Photo: Bronwyn Webby

MetService has issued several severe weather warnings and watches across the country.

A red severe thunderstorm warning is in place for Thames Coromandel, Waikato, Hauraki, Western Bay of Plenty, Matamata Piako, and Franklin.

A severe thunderstorm watch is in place for Auckland. Earlier parts of Northland and Auckland were under a severe thunderstorm warning, however this has been lifted.

Meanwhile, a heavy snow watch has been issued for Central Otago, Southland north of Lumsden, also inland Dunedin and Clutha until noon Saturday.

Orange heavy rain warnings:

Heavy rain watches:

Flooding over Brightwater.

Flooding over Brightwater, Tasman district. Photo: Charlotte Bacon / supplied

The top of the South Island is cut off at the moment with a number of state highways closed.

NZ Transport Agency is warning drivers to be prepared for wet weather driving and to take extra care on the roads.

FENZ Steve Trigg warned people not to drive through floodwater and to respect all "road closed" signs.

"It's impossible to judge the depth of the water, so when people become stranded they are in danger of drowning."

Here is a list of the highways closed:

Roads closed in Marlborough include:

Dozens of domestic flights bound for or departing from Auckland Airport have been cancelled or delayed due to severe weather conditions.

Auckland Airport said 21 flights have been cancelled and 11 flights have been delayed.

It said the weather is mostly impacting flights to or from regional destinations.

The airport also confirmed that a China Eastern Airlines flight from Hangzhou to Auckland has been diverted to Christchurch due to the unsettled weather conditions. China Eastern Airlines also confirmed the diversion.

No metadata