Young New Zealanders have become less exposed to second-hand smoke in their homes and while travelling in cars, research has found.

But surveys with year 11 students, found 35 per cent still being exposed to second-hand smoke in their homes and 32 per cent in vehicles in the latest survey in 2008. Exposure in homes and vehicles was above 40 per cent in 2004.

The surveys also showed total smoking bans inside and outside homes increased from 17 per cent in 2004 to 31 per cent in 2008.

The study, published in Friday's issue of the New Zealand Medical Journal, says second-hand smoke has been estimated to kill around 300 people in New Zealand annually.

Young people's exposure increases the risk of respiratory illnesses, ear problems, asthma, lung function and poorer mental health.

A greater risk of exposure has been found in low income homes, and among Maori and Pacific Islanders.

The researchers, from Otago University and the Health Sponsorship Council, say although more families are implementing home smoking restrictions, tougher measures are needed to reduce second-hand smoke (SHS) exposure for young people.

"These might include extending initiatives to reduce smoking in various settings such as cars, parks, beaches and shopping areas, and the provision of continuing education about the adverse health effects of SHS," they said.

The report follows budget tax hikes to lift the price of a packet of cigarettes to $20 by 2016, as part of the government's target of making New Zealand smoke-free by 2025.