An Auckland school has stopped its children going on beach trips after alarm at bits of building material with asbestos in it washing up.

Almost 200 schools were sent a warning sign by the Education Ministry earlier this week.

Glendowie School took immediate action.

"Based on [that] ... we have taken the step to discontinue any trips that involve direct contact with our local beaches, until such time that we know it is safe to return to those spaces," said principal Dr Paul Crowhurst.

Thousands of small pieces of asbestos-containing fibre cement board have been littering the sand around Tāmaki Estuary on various beaches.

"There are a lot of very, very concerned residents," said the chair of Tāmaki Estuary Protection Society, Dr Julie Chambers.

"We've been aware of this material washing onto the beach for some years but hadn't realised that it wasn't being investigated."

The council says it cleaned up Glendowie and Karaka beaches recently and that the risk was "negligible".

"The risk ... is considered extremely low to beach-users but we are taking a precautionary approach," said its general manager of licensing and compliance, Robert Irvine, in a statement.

The material was "non-friable" - not causing dust that could become airborne, which is when asbestos gets dangerous and can kill if inhaled.

"We are continuing to inform the Medical Officer of Health and receive advice ... on this matter."

The council had put up notices, was monitoring other beaches to see if the problem was widespread, and is advising people not to touch the material, which are mostly pieces smaller than the palm of a hand.

It recently removed the material from beaches in Glendowie and Karaka.

Some locals feel the council is not taking it seriously enough.

Asbestos found at Tāmaki Estuary. - Supplied via RNZ

"The council has made no attempt to contact any local schools, nature schools, ECE [early childhood education] groups or community groups that use these areas," said one local, who asked not to be named, about the situation prior to the notices that went out this week.

The ministry said it notified 197 schools as a "duty of care".

"We are aware that local schools and Early Childhood Centres use these areas, including for beach clean-ups," it emailed them on Tuesday, advising them to avoid contact.

The council had alerted the ministry earlier this week.

Locals say they first alerted the council in 2021, but then in steady manner since early February this year.