An early spike in the number of people needing hospital treatment for pneumonia is worrying doctors.

In the four months to April, more than 3300 people needed in-patient treatment for the disease.

Year-on-year figures show the number of people hospitalised with pneumonia has consistently increased each year since 2005, from 10,540 cases to 14,393 in 2014.

Elderly were most susceptible.

Starship Hospita'sl Dr Cameron Grant reports it's early in the year for a peak - which doesn't usually come until July or August - and staff are nervous about what's to come.

Dr Grant adds New Zealand's high rates of obesity and nutrient deficiency probably contribute to people getting infections easily.

Factors such as damp housing and people not getting vaccinated are also playing a part.

Pneumonia killed 3225 New Zealanders between 2005-2011, the ministry revealed, but data for the number of deaths over the past 3½ years was not available.