Health authorities in Japan are sounding the alarm about influenza. They say the average number of cases per medical institution has surpassed the warning level at the fastest pace in 10 years.

The National Institute of Infectious Diseases and other entities say about 5,000 medical institutions nationwide reported 166,690 flu patients in the seven-day period through December 10.

The figure is up more than 34,000 from the previous week.

The average number of patients per institution stood at 33.72, surpassing the warning level of 30 for the first time this season.

The estimated number of patients nationwide for the week ending Sunday is 1.11 million. The cumulative number of patients since September 4 is estimated at 8 million.

Thirsty-three of the country's 47 prefectures exceeded the warning level, including Hokkaido with 60.97.

Thirteen prefectures have surpassed the threshold of 10 for an advisory, including Osaka with 22.2, and Tokyo with 20.3.