A dramatic rescue in heavy seas saw three people saved from near-drowning near Whitianga yesterday.

Two men and a woman were close to drowning after their boat sank in heavy seas and rescuers said they owed their lives to the crew of a passing vessel.

TrustPower rescue helicopter pilot manager Liam Brettkelly said a Hamilton man, 66, an Auckland man, 52, and an Auckland woman, 49, spent a frightening hour in the water about 1km off the coast when two people in a glass-bottomed tourist boat spotted them by chance.

"It was very lucky because that boat had only just happened to come across one of them.

"It had gone right past two of them," Mr Brettkelly said.

The trio's 4.2m boat was swamped by a large wave about midday but they managed to get a mayday call out before the vessel went down.

They were all flown to Tauranga Hospital suffering from hypothermia but were later reported to be in a moderate condition.

Mr Brettkelly said the sea was rough with strong winds.

"I can't imagine it was much of a day for sightseeing."

Further north at Ruakaka in Northland a large search was launched for two divers reported missing after failing to return on time.

The missing divers were found without incident, police said.

Meanwhile, holidaymakers who left the trip home until late in the day faced heavy delays and treacherous driving conditions as rain fell over much of the North Island.

Heavy falls affected Taranaki, Manawatu, Wellington and the Marlborough Sounds.

That caused slips, surface flooding and road closures in Manawatu and Wellington. Flooding closed SH56 east of Foxton with diversions in place.

Motorists heading back to Auckland on SH1 from Northland faced queues north of Wellsford but conditions eased after many took the alternative route south on SH16.

Police had urged motorists returning to Auckland from the north to delay their trips if possible as lines of traffic moved bumper-to-bumper on some sections of the highway.

The Southern Motorway became heavy in the early evening but police reported no major problems.

An accident forced police to close the road between Coroglen and Whenuakite on the Coromandel Peninsula and advised motorists to use alternative routes southbound from Whitianga on SH25.

The rain was forecast to get heavier in the lower North and upper South Island as the day wore on.

At Ruakaka in Northland, a woman phoned police when two divers who had been on her vessel failed to return to the boat on time. A police Eagle helicopter and the Northland rescue helicopter responded, with a coastguard vessel and other boats.

Police said the missing divers were found without incident.

Windsurfers made the most of blustery conditions on Auckland's Waitemata Harbour, but boaties stayed at home or sat tight as a wind warning was issued for much of the Hauraki Gulf. A storm warning was issued for Cook Strait last night.

Cold southerlies rising to gales in exposed places were forecast for Banks Peninsula, northern Canterbury and the Kaikoura Coast overnight with snowfalls possible today.

Rain was again expected to be widespread over much of the North Island as the low pressure system that brought the damp weather travelled southeast and was expected to lie east of Wairarapa today.