Parents face tough choices over their children's education after health authorities declared large parts of Auckland unsafe for early childcare centres because of pollution.

Concerns about health risks for young children mean new centres are unlikely to get medical approval to open within newly created "buffer zones".

Existing centres may come under pressure to move if they fall within the zones.

The zones have been created by the Auckland Regional Public Health Service. They cover areas within 300m of an industrial zone, 150m of a motorway or truck route, 100m of a petrol station and 60m of a main district road.

New childcare centres need a positive health report from the Director-General of Health when applying to the Education Ministry for a licence.

The Public Health Service carries out checks for the Director-General.

Service clinical director Julia Peters said research showed children aged 18 months and younger were especially vulnerable to the effects of pollution because their lungs were still developing.

Children within the buffer zones faced a greater risk of respiratory infections and asthma, and could suffer reduced lung function.

Those at centres near petrol stations were also at increased risk of developing childhood leukaemia because of benzine concentrations.

"My advice to parents is they take a close interest in where they are sending there children," said Peters.

Asked if she would send her children to centres inside the zones, she replied: "I'd make every effort not to."

The Auckland area has 105,000 children aged 4 and under, of which about 40,000 are in early childhood centres for an average 21 hours each week.

At least three new centres have already been refused a licence because of air-quality concerns.

Two belong to Kidicorp, a major early childhood operator with 37 centres in Auckland.

Edu Kids Manukau, originally called Jump & Jive, was unable to open in 2007 because of concerns about its location on a busy intersection near a petrol station.

It is operating on a provisional licence pending the results of air monitoring by the Health Ministry.

Kidicorp licensee Fiona Hughes said she was confident the results would show the air quality met national environmental standards set by the Environment Ministry.

The centre wrote to parents answering questions over the air quality, but parents were not alarmed.