A spokesman for Royal Prince Alfred Hospital confirmed the deaths.

"One person is still receiving treatment, but two people have passed away," he said.

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The spokesman said he was not yet able to provide details about their ages or genders, but the Canberra Times reported that all were believed to be Chinese nationals.

A total of four people were taken to hospital after eating the mushrooms at a party in Canberra, heath authorities said.

A 52-year-old woman and a 38-year-old man were flown to Royal Prince Alfred Hospital in a critical condition from Canberra's Calvary Hospital on Monday afternoon, a Calvary spokesman said.

A 51-year-old man was taken to Royal Prince Alfred in a critical condition from Manly Hospital, a spokeswoman for Northern Sydney Health Service said.

The fourth patient, a man, was discharged from Canberra Hospital yesterday, a spokeswoman said.

In a statement this afternoon, Sydney Local Health District said the man still being treated at RPA after eating the mushroom was in a critical but stable condition. The statement warned that eating just one of the mushrooms can be fatal.

Director of Emergency at Canberra Hospital, Dr Michael Hall, said the patient discharged yesterday was fine, and would not have any long-term problems from the poisoning.

"We believe that he had a much smaller serve of a mushroom-prepared meal," he said.

The mushrooms tend to grow around Canberra and in southern NSW and are most often found at the bottom of oak trees.

Death cap mushrooms are filled with amatoxin, which can attack enzymes involved in producing DNA.

The poison can also trigger liver failure.

It is not known if the mushrooms were picked or bought before the poisoning in Canberra.

A statement from ACT Health, released this week, said three people had died from eating death cap mushrooms in the past decade and there had been about 12 reported cases of poisoning.

A spokesman for ACT Policing said NSW Police would prepare a report for the coroner, but the matter was not the subject of a police investigation.

"The matter may be referred to us to have a look at the circumstances," he said.

"[But] until we receive a formal request, no."

For Australian government information on death cap mushrooms - click here.

- with Stephanie Anderson, Canberra Times