More than 20,000 attended the 16th annual Rhythm and Vines festival last summer.

Dangerous drugs, made with pesticides and paints, have been found at Rhythm and Vines.

A police email said the drugs were fake MDMA tablets, containing pesticides, antibiotics and traces of paint. It was unclear how much was seized.

Organisers of the annual New Year's festival near Gisborne issued a warning to its thousands of punters to be wary, after authorities seized the dangerous drugs on Monday.

SUPPLIED Rhythm and Vines has issued a health warning to its customers.

The warning was push-notified to customers' phones, after authorities tested the seized drugs. Rhythm and Vines event manager Dan Turner said the festival issued the warning so its patrons would know as soon as possible about the drugs.

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"We're trying to educate the kids, to say 'look, what you're taking may not be what you think it is'. That's what we tried to achieve with the push-notification," he said.

Anyone who had taken drugs, and felt unwell, was urged to seek medical attention. About 21,000 festival-goers started to arrive on Friday. including the 14,000 people camping on site.

The St John medical tent at Rhythm and Vines had seen some people reacting badly to drugs at the festival, but none of those patients had needed hospital attention.

Turner said the drugs were found during a car check, on entry to the festival on Sunday morning. Security have been checking cars and bags on entry.

The warning, from the Tairāwhiti DHB, said the seized drugs contained industrial paint compounds, pesticides and other dangerous compounds.

Police said they had made no drug related arrests at Rhythm and Vines. A spokesman said they were happy with behaviour so far at the festival.

St John Tairāwhiti territory manager Shane Clapperton said his team had been "flat out" at Rhythm and Vines, but this year had not been unusual.

Between 7pm and 8pm on Sunday, December 30, the St John medical tent saw 50 people. Many of the people needing attention had minor issues, he said. However, four people were sent to hospital on the first two days of the festival. Those patients had been injured on site.

The health warning was issued as the headline acts kicked off on New Year's Eve.

Tairāwhiti DHB have been contacted for further comment.

The three-night festival, which has been run for the past 16 years, ends in the early hours of New Year's Day.