Some ferries across Auckland's Waitemata Harbour have been cancelled this morning as the top of the country remains under a heavy rain alert.

A severe weather watch is in force for Northland, Auckland north of Orewa and Great Barrier Island until later this morning.

In the past 12 hours up to 30mm of rain has fallen across Northland and up to 10mm in Auckland.

The front containing thunderstorms is moving slowly south this morning before it weakens.

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MetService says bursts of heavy rain are possible and some downpours may reach warning criteria.

This morning Auckland Transport cancelled all Gulf Harbour ferries because of bad weather and replacement buses will take passengers between Auckland and Whangaparaoa.

Further south slips have closed several roads across the Whanganui region.

Council crews are clearing debris from four roads after heavy rain lashed the region this week.

Manawatu Wanganui Civil Defence said Kauarapaoa and Creek Rds were expected to be re-opened by lunchtime.

Burma Hill Rd on the Mangamahu side was closed but debris was expected to be cleared by the end of the day.

Crews were also clearing a fourth slip affecting Mangamahu Rd but it was not known how long the operation would take.

Today's forecast

Auckland:

Occasional rain, clearing this morning. Fresh southeasterlies. 14C

Hamilton:

Cloudly, showers then fine. Southeasterlies weakening. 15C

Tauranga:

Morning showers then fine. Southeasterlies easing at night. 14C

Wellington:

Cloudy, showers. Fresh southerlies. 9C

Christchurch:

Cloudy, showers, light winds. 8C

Dunedin:

Morning cloud then fine. Northeast breezes. 8C