The leader of Komeito, the smaller party in Japan's ruling coalition, said Thursday barring spectators from the Tokyo Olympics should remain an option amid concerns of a sharp rebound in coronavirus cases.

Natsuo Yamaguchi's remarks come as Prime Minister Yoshihide Suga mulls whether to extend a quasi-state of emergency covering the capital and surrounding prefectures with less than a month until the games begin.

Natsuo Yamaguchi. (Kyodo)

"I've said we need to be on the lookout for a rebound in infections, and that's exactly what we are seeing now," Yamaguchi told reporters. "I hope the government will remain open to the possibility of there being no spectators and inform the public of any decisions in a timely manner."

While Suga's top COVID-19 adviser, Shigeru Omi, and other infectious disease experts have said holding the Olympics and Paralympics without fans is the "safest option," organizers have agreed to fill venues to 50 percent capacity, with an upper limit of 10,000 spectators.

The attendance cap is contingent on Tokyo and other prefectures where the games will be held exiting the quasi-state of emergency, currently due to expire July 11.

Yamaguchi said the government should decide whether an extension is necessary after consulting with experts.