Up to 12,000 visitors to Yosemite national park in California may have been exposed to a deadly mouse-borne virus that has already claimed two lives.

The mice nested in the cavity walls of insulated tents and the virus was spread through their faeces, saliva and urine.

The company that operates the tents contacted 3,000 people who made reservations during the summer. A further 9,000 could have also stayed in the tents.

On Thursday, the California department of public health confirmed that six people had contracted the hantavirus pulmonary syndrome at Yosemite, up from four suspected cases earlier in the week, and the centres for disease control and prevention said they have identified other possible cases of the virus which have yet to be confirmed.

The illness begins with flu-like symptoms and can take six weeks to incubate before rapid acute respiratory and organ failure.

There is no cure, and anyone exhibiting the symptoms must be hospitalised. About 36% of people who contract the rare illness will die from it.

All of the victims of the virus stayed in specific four-man tents in the Curry Village area of the park between mid-June and early July