California is facing what could be its largest toxic mushroom outbreak in history, with three deaths and more than 30 people sickened after consuming poisonous fungi.

Heavy rains and mild weather have caused death cap and Western destroying angel mushrooms to flourish, particularly in Northern California.

Between November 18 and January 4, 35 mushroom poisoning cases were reported, including three that required liver transplants.

Officials warn that toxic mushrooms often resemble edible varieties and advise against foraging or buying wild mushrooms from unverified sources, ABC News has reported.

Early symptoms include nausea, vomiting, diarrhea, and abdominal pain, and effects may not appear until six to 24 hours after ingestion.