NEW YORK/ANCHORAGE, Alaska (Reuters) - Several workers on a BP Plc oil platform in the U.S. Gulf of Mexico have tested positive for coronavirus, the company said on Wednesday, a day after a worker at BP’s operations in Alaska also tested positive.

The cases are the first recorded among oil workers in the Gulf of Mexico and Alaska, and follow a positive test at an Equinor offshore project in the North Sea.

A case of the coronavirus was also reported at BP’s Whiting, Indiana refinery, according to local media reports.

More than 850,000 people have been infected by the virus worldwide, which has killed more than 42,000 people.

The disease outbreak presents special challenges for oil companies’ offshore platforms and other isolated locales. Such facilities bring workers in and out on a rotating basis, keeping them in place for a designated time before new workers replace them.

BP and other companies have already extended their designated work periods to limit travel.

The worker who tested positive at BP’s operation in Alaska’s Prudhoe Bay has been isolated, the state’s chief medical officer said. The worker was an Alaska resident who had recently traveled out of state, its department of health and social services said in a statement.

“BP is following procedures and protocols to minimize the risk of COVID-19 and ensure the safety of our people. We are eliminating all non-essential activity on the slope,” said Megan Baldino, spokeswoman for BP Alaska.

The BP worker had returned to Alaska before travel curbs imposed on March 23, going to the North Slhope on March 25.

BP gave no details on which platform the Gulf of Mexico case was associated with, and had no immediate comment on potential production cuts in response to the cases.

But the company said in a statement that it had instituted additional cleaning and other sanitation measures to keep its workers safe during the outbreak.