A Hamilton teenager with swine flu died at home without being diagnosed with the illness.

He was one three New Zealanders to have died in the past week with swine flu more than likely to have been the cause, the Ministry of Health confirmed today.

Zachary Wilson, 19, had been ill for three or four days but had not been to hospital before he died last Sunday, said Waikato District Health Board medical officer of health Dr Felicity Dumble.

"What's become apparent with this situation is how quickly this can develop, and somebody can present with what looks like a common cold that may progress to more like influenza and then it can rapidly become something very serious."

Some efforts were made to treat Mr Wilson's symptoms, although no further details were made available.

Mr Wilson's family, who had been devastated by his death, wanted people to be aware how quickly someone's condition could deteriorate, Dr Dumble told reporters.

Given the wide spread of swine flu, health authorities were focusing on treating people who were sick rather than routine testing.

Mr Wilson's case of swine flu was discovered following an autopsy.

The coroner would examine if any other medical conditions had played a part in Mr Wilson's death, she said.

However, he had a history of asthma which, along with other factors such as diabetes and cardiovascular conditions, was more likely to cause complications.

Although people had been advised to stay at home if possible to avoid spreading the illness and adding to pressure on the health system, anyone whose condition worsened should seek medical attention, Dr Dumble said.

Some deaths were expected as a result of swine flu, she said.

"It's really important that people are aware that influenza is a serious illness and it does kill."

Signs to look watch out for included a rapidly worsening condition, a difficulty being woken, confusion or irritability, a fever of about 38.3 degrees, fits, and not keeping down fluids.

Chief Coroner Neil MacLean said a 42-year-old man with underlying medical conditions had also died on Thursday in Christchurch.

It was "strongly probable" that the H1N1 virus (swine flu) was a major factor in the deaths of both men, he said.

Meanwhile, Capital and Coast District Health Board said a young girl with underlying medical conditions died this morning in Wellington Hospital. She had earlier tested positive to swine flu.

Health Minister Tony Ryall said he, along with the ministry, expressed sincere condolences to each of the families involved.

Swine flu continued to spread throughout the community and would be around for some time, but there was no cause for alarm, Mr Ryall said.

Director of Public Health Mark Jacobs said there was no need for New Zealand health authorities to change their management approach at this stage, but vigilance would remain.

"For most New Zealanders, swine flu will be a mild illness, but in some instances, the infection can cause more severe illness and in a few tragic instances, death," he said.

As of today, the total number of confirmed cases in New Zealand was 945, up from 912 yesterday.

The cumulative total of confirmed cases by region are: Northland (20), Auckland (202), Waikato (45), Bay of Plenty/Lakes (29), Gisborne (2), Hawkes Bay (75), Taranaki (3), Wanganui/Palmerston North (14), Wellington (292), Nelson/Marlborough (19), Canterbury (230), Otago/Southland (14).

- NZPA