TOKYO -- The outbreak of the new coronavirus in Japan has renewed calls in political circles to commission hospital ships for treatment offshore in times of emergency.

Two such vessels are said to be sufficient to reach a trouble spot in Japan within 24 hours. But the Self-Defense Forces do not have any dedicated hospital ships.

In hopes of addressing this, an interparty caucus of about 40 lawmakers that have been pushing for the ships met for the first time in seven years Tuesday.

"We ask the government for a budget that completes the design of new ships in fiscal 2020 so that they can begin service in fiscal 2023," said Seishiro Eto, chairman of the hospital ship caucus, who called for research funds.

Another group of lawmakers formed on Thursday goes even further and advocates repurposing private-sector vessels as hospital ships in addition to the construction of new ships.

The concept has been floated in times of disaster, such as the March 2011 earthquake and tsunami. A 2013 government report noted that hospital ships serve key functions in such times.

Hospital ships once again gained currency when hundreds of passengers on the Diamond Princess cruise ship contracted COVID-19. The vessels would be useful options for treating patients while they are quarantined.

But expense is an issue. The Cabinet Office estimates that a single hospital ship costs 35 billion yen ($324 million) to build and 2.5 billion yen a year to operate and maintain. And in normal times, the ships see only limited use.

The Geneva Conventions define a dedicated military hospital ship as a vessel built or equipped "solely with a view to assisting the wounded, sick and shipwrecked, to treating them and to transporting them." The U.S., Chinese and Russian navies field hospital ships that are protected by the conventions.

In Japan, there are no dedicated hospital ships. The destroyer Izumo and the supply ship Mashu are equipped with intensive care units and hospital beds. Training is carried out to load medical supplies onto SDF ships.

Inside the ruling coalition there are calls for equipping self-defense ships so that they can be used as hospital ships while working to quickly introduce dedicated vessels that can respond to large-scale disasters.