SA Health has highlighted dangerous fungi after the Poisons Information Hotline received an increasing number of calls, beginning earlier than normal.

So far, about two-thirds of all calls were related to children aged under five years, with five of them referred to hospital.

The health department's Scientific Services Branch Director David Simon said some wild mushrooms looked similar to those sold in supermarkets but eating them could cause serious illness or even death.

"It's especially important to keep an eye on children and pets outside as mushrooms are easily in reach and can look interesting and attractive to eat," Dr Simon said.

"We need to look out for each other and keep each other safe and out of hospital, particularly right now in the middle of the COVID-19 pandemic and with flu season just around the corner."

It can take a few hours for symptoms to appear which can last for up to three days.

Signs of mushroom poisoning include violent stomach cramps, abdominal pain, nausea, vomiting and diarrhoea.

Australian Associated Press