A warning has been issued in Christchurch after drug checking services discovered samples believed to be methamphetamine were actually glass.

High Alert, New Zealand’s drug warning service, said several unusual samples had recently been brought in for testing.

The material reportedly looked like methamphetamine but did not behave like the drug when examined.

High Alert said the samples would not melt in a pipe, dissolve in water or crush easily.

The organisation is urging people not to assume substances are what they appear to be and to have anything suspicious checked.

High Alert encouraged people to visit local drug checking services if they are uncertain about a substance.

Rodger Wright Harm Reduction Network operates a free, confidential drug checking service at 10 Washington Way in Sydenham, Christchurch.

The organisation is a licensed drug checking provider and offers testing and advice aimed at reducing drug related harm.

High Alert said people who experience unexpected or unusual effects after taking a substance can report them through its website.