Death cap mushroom season has arrived early in the ACT this year, with authorities warning Canberrans the best way to avoid poisoning from the dangerous fungi is to steer clear of picking wild mushrooms all together.

Four people in the ACT have died from eating death cap mushrooms in the past 15 years, with more treated for poisoning.

The mushrooms are usually found during autumn, but the ACT's chief health officer Paul Kelly said wet weather and cool nights had prompted their early arrival in 2015.

Dr Kelly said people should avoid picking any wild mushrooms, as death caps were easily confused with edible varieties.

"Unfortunately the poison in the death caps cannot be destroyed by cooking, so eating death caps raw or cooked are still poisonous," he said.

"They [poisoning victims] start with a typical gastro-enteritis type illness with stomach pains, nausea, vomiting and diarrhoea. But they can if you eat enough of it, lead on to liver failure and even death."

Last year four death cap poisoning cases were reported by authorities, with all of the victims suspected of harvesting and eating wild mushrooms.

Dr Kelly said anyone who suspects that they might have eaten death cap mushrooms should seek urgent medical attention at a hospital emergency department.

"The sooner treatment begins, the better the patient's chances of survival," he said.

What does a death cap mushroom look like?

Death caps look similar to the straw mushroom from Asia and are common in many Canberra suburbs.

Death cap season does not usually start until Autumn, but these mushrooms were spotted in Yarralumla on Saturday. ( ABC News: Anna Morozow )

They can be found growing near established oak trees during warm, wet weather.

The caps of the mushrooms are 40-160mm wide, usually pale green to yellow in colour, with distinctive white gills and white stem.

It has a membranous skirt on the upper part of the stem and a cup-like structure around the base of the stem (called a volva).

Sometimes the bulbous base and the volva are partially buried in the soil or hidden by grass and leaf litter.

The cap may be slippery and sticky to touch and shiny when dry.