Japan's Foreign Minister has expressed concern over China's advances in the South China Sea at the East Asia Summit with his counterparts.

Toshimitsu Motegi took part in the online meeting held late Wednesday, Japan time. The event was attended by foreign ministers of the 10-member Association of Southeast Asian Nations, as well as Japan, China, the United States, Russia and others.

Japanese Prime Minister Abe Shinzo spent three and a half hours at a hospital in Tokyo on Monday for medical reasons. He says it was a follow-up to a test he took last week. But the visit adds fuel to concerns the prime minister may be in poor health.

Abe said, " I heard details about my test results and also underwent additional tests. I'll continue to do my best in my work and take all measures to manage my physical condition."

Chief Cabinet Secretary Suga Yoshihide says the Japanese government continues to watch the situation in Hong Kong with grave concern.

Suga spoke to reporters on Tuesday after Hong Kong police arrested pro-democracy activists and a media tycoon under the territory's new national security law.

Japan's foreign minister has conveyed concerns to his Chinese counterpart over Beijing's introduction of a national security law for Hong Kong.

Motegi Toshimitsu talked with Chinese Foreign Minister Wang Yi by phone on Wednesday. The talks took place at the request of Chinese authorities.

Experts working for the Tokyo Metropolitan Government have raised the level of concern about the coronavirus outbreak in the city to the highest level. They used strong language when stating that the virus appears to be spreading.

The experts raised the level from three to four on the Tokyo Metropolitan Government's four-tier scale.

Japan's finance minister Taro Aso has warned his G20 counterparts about digital currency, saying more work is needed before any issuance.

In a news conference after the meeting of the Group of 20 finance ministers and central bank chiefs in Saudi Arabia, Aso said regulations on digital currency should be drawn up to avoid potential risks such as money laundering.