Tokyo Gov. Yuriko Koike triggered the Tokyo Alert system for the first time Tuesday night following an uptick in new coronavirus patients, but some experts have expressed doubt over the effectiveness of the warning mechanism.

Tokyo Alert was introduced more than two weeks ago as part of the city’s plan to gradually reopen society while preventing a second wave of infections.

Koike said she would consider issuing an alert if the average daily number of new cases exceed 20 in a week, the average number of untraceable cases was higher than 50 percent and the number of new cases was more than double that of the previous week.