New Zealand food safety experts say they are "struggling" to determine a safe level of melamine in the nation's diet, but have opted for a threshold of 5 parts per million.

The New Zealand Food Safety Authority (NZFSA) today said that melamine now appeared to be widespread in the food chain, but claimed it was harmless at low levels.

"We know that the presence of this chemical is part and parcel of our life today, apparently leaching from plastics and contact materials during processing and packaging in trace quantities," said NZFSA director of compliance and investigation Dr Geoff Allen.

"At low levels it causes us no harm," he said.

"Determining just how high levels have to be before there is a risk is something we are all struggling with."

Eating high levels of melamine is thought to cause kidney stones and can ultimately result in kidney failure.

The highest reported levels of melamine in Chinese infant formula are around 2500mg/kg and four children have died and almost 53,000 have been made ill after consuming infant formula.

The contamination was first discovered in products made by Fonterra's joint venture partner in China, Sanlu.

Last night, the European Food Safety Authority (EFSA) confirmed its estimated tolerable daily intake (TDI) of melamine at 0.5mg/kg - effectively saying a person can safely eat 0.5mg of melamine each day for each kilogram of bodyweight.

This means a 20kg child could safely eat 10mg a day and a 70kg adult 35mg.

Though milkpowders, including infant formula, and liquid milk have been the main contamination pathway in China, agencies in Western nations have become more concerned about food categories that use milk powder as an ingredient, particularly chocolate and biscuits.

The EFSA ruled that in a "worst case scenario" European children would eat triple the tolerable daily intake of melamine chemical even if they were only exposed to contaminated milk powder in biscuits, chocolate and other foods.

In New Zealand, this concern was highlighted when retail chain The Warehouse, noted for selling a wide range of goods from China, today pulled from sale four biscuits and sweets containing Chinese milkpowder.

It said the removal of Cherir I Love You chocolate rose, Oreo brand children's biscuits, Mr Mallow bagged confectionery, and a novelty sweet Au Some "mini frooze pop" was "precautionary" with no evidence they were actually contaminated.

NZFSA said today its 5ppm threshold was "conservative": "Foods containing up to 5ppm of melamine do not pose a risk to human health".

Dr Allen said the authority built in safety factors by assuming in its calculations that all of the food a person ate contained melamine, and then used the level which would be safe for a child aged six months to a year old.