Authorities are warning about poisonous deathcap mushrooms which thrive near oak trees in warm and wet weather, typical at the end of summer and early autumn.

With a warmer-than-usual autumn on the way, a leading food safety authority is warning about the potentially fatal deathcap mushroom.

Nine out of 10 mushroom poisonings are caused by the introduced wild species, which largely grows in the ACT and around Melbourne and can be mistaken for more common varieties that are safe to eat.

Four people have died in the part 16 years after eating deathcap mushrooms, including two who were served the fungi at a New Year's Eve party at Canberra in 2012.

The Bureau of Meteorology has forecast a warmer-than-usual autumn across Australia which may aid the mushroom's growth.

"These mushrooms start to appear this time of year," Food Safety Information Council Chair Rachelle Williams said.

"Deathcap mushrooms are difficult to distinguish from other wild mushrooms so we recommend you play it safe and only eat mushrooms that you have purchased from the supermarket."

Deathcap mushrooms thrive near oak trees in warm and wet weather, typically at the end of summer and early autumn.

Fully grown, they have a silky smooth cap and vary from white to greenish-brown with white gills and can easily be mistaken for several Asian varieties.

The fungi's toxin can't be removed by cooking and can cause vomiting and stomach cramps, and potentially be lethal without proper medical treatment.

"Many cases of reported fungi poisoning are in children under five years of age," Ms Williams said.

"Most young children who eat poisonous mushrooms find them in the garden at home."

The deathcap is widespread across Europe and likely came to Australia attached to oak trees.

A similar marbled variety has recently been found in Western Australia.