The measures come as the country recorded 300,000 new coronavirus cases with the death toll reaching 4,187.
Niinami suggested the fate of the Games was likely be decided by the end of March, where the results of Government efforts to curb the spread of coronavirus are expected to be known.
Media reports also said Tochigi and Fukuoka prefectures would be brought under the declaration, too, after they called on the central government on Tuesday to expand the state of emergency there.
The emergency declaration, covering 55% of Japan's population of 126 million, is set to last through February 7 and is much narrower in scope than the first one last spring.
"To protect people's lives and livelihoods, and to remove potential risks (over the pandemic), I have made a decision to temporarily suspend the entry of foreign business travellers", Suga said.
But lawmakers within his Liberal Democratic Party had pushed for the exemption to be suspended, arguing it was contradictory to ask Japanese people to stay home under the state of emergency while allowing non-resident foreign nationals into the country.
But Kato said Suga did not make that comment to Gates.
A rise in coronavirus cases in Tokyo has led to a state of emergency being introduced in the Japanese capital
Nagahama said in a report his estimate also reflects the impact of the suspension since December 28 of the Go To Travel campaign, a government-subsidized program meant to boost the virus-hit domestic tourism sector. Suga will hold a news conference at 7 p.m. (1000 GMT).
Political analyst Atsuo Ito said he saw two major problems with Suga's response to the pandemic: that it was incremental and slow, and that he was a poor communicator.
"He has nearly no skill at messaging".
Toshio Nakagawa, the association's president, raised the prospect at a January 13 news conference to help alleviate some of the pressure on the health care system. That doesn't invite trust from citizens.
Suga's approval rate fell below those who disapproved for the first time in an NHK poll since he took office in September - by 40% to 41%.
"It's very unlikely we'll see cases go down after just a month", said Yoshihito Niki, an infectious disease specialist and professor at Showa University Hospital. But polls have shown the public's hope for the Games has faded.
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