Tokyo has been put on the highest level of alert for the coronavirus after a string of triple-digit new daily cases. Officials are urging people to take precautionary measures.
Tokyo Governor Koike Yuriko said, "We decided that we need to raise the alert level to warn residents that infection is spreading."
More than 200 cases were reported for four days in a row through Sunday.
Since then, numbers have dipped slightly but are still topping 100, with 165 cases reported on Wednesday.
Experts are especially concerned about the increasing number of untraceable cases.
The weekly average has nearly doubled recently.
Disease Control and Prevention Center Director Ohmagari Norio said, "In four weeks, the number of untraceable cases could be 16 times as many as now. That means about 1,200 people. If it continues to double, eight weeks from now, the figure will increase by 256-fold."
The governor is calling on residents to refrain from non-essential travel to other prefectures.
She is also asking people not to visit restaurants and night clubs not taking sufficient anti-virus measures.
The number of infections continues to rise in other parts of Japan.
Sixty-one cases were confirmed in the western prefecture of Osaka on Wednesday.
That's the highest since a nationwide state of emergency was lifted in May.
Across Japan, more than 22,000 people have tested positive for the coronavirus.
Nearly 1,000 people have died.
Officials are also closely watching developments in the southern prefecture of Okinawa, home to many US military bases. More than 130 personnel have been found to be infected there.
Okinawa Governor Tamaki Denny met Defense Minister Kono Taro in Tokyo. He asked the minister to push the US military to swiftly provide detailed information on the infected people.
Tamaki said, "I hope he will tell the US side what he has to say as Japan's defense minister, whose duty is to protect the people of this country. I also want him to consider the position of the local governments that host the US bases."