People still in quarantine due to fears of the new COVID-19 coronavirus stand on the deck of the Diamond Princess cruise ship docked at the Daikoku Pier Cruise Terminal in Yokohama on February 18, 2020. Photo: AFP

 
Japan plans to trial HIV medications to treat patients infected with coronavirus as its growing number of cases poses an increasing threat to the economy and public health, the government's top spokesman said on Tuesday.

The government was making "preparations so that clinical trials using HIV medication on the novel coronavirus can start as soon as possible," Yoshihide Suga told a briefing, but added he could not say how long a new drug would take to be approved.

Japan had 520 confirmed infections by Monday, including 454 cases from the Diamond Princess cruise ship quarantined off the port of Yokohama, the health ministry said, with one death from the virus. 

On Tuesday, there were three more cases confirmed with the virus in Wakayama Prefecture, local media reported.

As the contracting economy fuels a risk of recession, the spread of the virus has prompted Tokyo to put limits on the size of public gatherings while some companies are telling employees to work from home.

The HIV trials come as those drugs have been touted as a potential cure for the coronavirus around the world. 

With no therapy yet proven 100 percent effective, the epidemic has killed more than 1,800 people in Chinese mainland.

In Thailand, doctors said they appeared to have had some success in treating severe cases of the virus with a combination of medications for flu and HIV. 

As demand for masks skyrockets, police are investigating a theft of 6,000 surgical masks reported by the Kobe Red Cross Hospital in the central Japanese city, a hospital official said.

Japanese officials have vowed to work hard to avoid disruptions to the Olympic Games, which start in Tokyo in July. But growing concern over the virus spurred Mongolia's Olympics archery team to cancel training in Japan, the Kyodo news agency said.

With more than 3,000 passengers and crew, the ship has been in quarantine since early this month, after a passenger who had left it in Hong Kong was diagnosed with the virus.

About half of those aboard are Japanese and the rest foreign nationals, many of whom have expressed frustration over the quarantine.

Disembarkation was set for Wednesday to Friday, Japan's vice health minister said, according to a copy of a letter circulated on Twitter by a passenger.