Japan's capital has reported 366 new coronavirus cases, Yuriko Koike, the governor of Tokyo, said on Thursday, a new daily record fuelling fears of a second round of infections.

As Japan began a four-day stretch of holidays, the city's government declared its highest alert against the disease. Thursday's figure took cumulative infections to more than 10,000 in Tokyo, topping a daily high of 293 cases last week.

"A total of 366 cases have turned positive, which was the largest number to date, and a record 4,926 were tested," Koike told reporters.

"It's a very big number. Please refrain from going out as much as possible during the four-day weekend. We must stop infections from spreading with everyone's cooperation."

Although Japan has suffered about 28,000 infections and more than 1,000 deaths, it has escaped the kind of explosive surge seen elsewhere.

But recent signs of a spurt in infections in Japan, as well as other major economies, such as the United States, have prompted authorities to raise renewed alerts against the virus.