"He is doing well and is responding to treatment," Domingo's spokesperson told CNN on Sunday.

On March 22, the 79-year-old Domingo revealed via his Facebook page that he had tested positive for COVID-19.

"I beg everyone to be extremely careful, follow the basic guidelines by washing your hands frequently, keeping at least a six-foot distance from others, doing everything you can to stop the virus from spreading and please, above all, stay home if you can," he wrote.

"Together we can fight this virus and stop the current worldwide crisis, so we can hopefully return to our normal daily lives very soon. Please follow your local government's guidelines and regulations for staying safe and protecting not just yourselves, but our entire community."

Days earlier, Domingo had resigned from the American Guild of Musical Artists. Two separate investigations, one by the Guild and another by Los Angeles Opera, of which Domingo was previously general director, found that sexual harassment charges against him were credible.

The investigations led to a string of cancellations of Domingo's European concert dates, including London's Royal Opera House and a concert organised by Spain's National Institute of Performing Arts and Music.

As he resigned from the guild, Domingo donated $US500,000 towards a program that looks to eliminate sexual harassment as well as a separate fund that supports opera workers in crisis.

Australian Associated Press