US health authorities are warning tourists who visited California's famous Yosemite National Park recently to beware of a rare virus spread in mouse droppings, after two people died.

A second fatality was confirmed at the weekend from "hantavirus pulmonary syndrome" (HPS), while two more people who visited the spectacular California park in June are being closely monitored.

The National Park Service wants to contact visitors who stayed in "Signature Tent Cabins" at Curry Village, an accommodation center in the vast park's Yosemite Valley tourist hub, since mid-June.

"These individuals are being informed of the recent cases and are being advised to seek immediate medical attention if they exhibit any symptoms of hantavirus," said an NPS statement.

Hantavirus is a rare but serious disease and early medical attention is "critical" to limit its effect. It begins with fever and aches, but can progress rapidly to a life-threatening illness, said the NPS.

HPS is caused by a virus that individuals get through contact with the urine, droppings or saliva of infected rodents, primarily deer mice.

Since the disease was first identified in 1993 there have been some 60 cases in California and 587 cases nationwide in the United States, around a third of which have been fatal.

"The health of our visitors is our paramount concern and we are making every effort to notify and inform our visitors of any potential illness," said Don Neubacher, Yosemite National Park Superintendent.

"Because people often don't get sick from hantavirus until one to six weeks after exposure, we are encouraging anyone who stayed in Curry Village since June to be aware of the symptoms of hantavirus and seek medical attention at the first sign of illness".