SYDNEY (Reuters) - Australian health authorities said on Saturday they had closed a clinic and were contacting around 70 patients of a doctor who has been diagnosed with coronavirus after recently returning from the United States.

The Melbourne-based general practioner returned to Australia on Feb. 29.

He became unwell with a runny nose on an internal flight from Denver to San Francisco before flying to Melbourne on United Airlines flight 0060, Victoria State Health Minister Jenny Mikakos told a televised news conference.

He saw about 70 patients between March 2 and March 6.

“The doctor...most likely acquired his infection in the United States,” Mikakos said.

“I have to say I am flabbergasted that a doctor that has flu-like symptoms has presented to work,” she said, adding the clinic has been closed until further notice.

Mikakos said patients have been contacted while the passengers on the flight will be contacted as soon as the manifest is available.

Four special coronavirus clinics have now been opened in Melbourne to reduce the strain on emergency departments and GP clinics.

New South Wales state reported six new cases of coronavirus overnight bringing the total cases in Australia to nearly 70.

Australia will release 260,000 surgical masks from medical stockpiles for immediate use, deputy chief medical officer Paul Kelly told a media briefing in Canberra.

The outbreak has killed more than 3,400 people and spread across more than 90 nations, with seven countries reporting their first cases on Friday. The economic damage has also intensified, with business districts starting to empty and stock markets continuing to tumble.