Two mayors have been dismissed in northeastern China, and Shanghai has closed its school system and shifted to online instruction, as a coronavirus outbreak in mainland China gathers speed.

China’s National Health Commission announced Saturday that another 1,524 locally transmitted coronavirus cases had been detected in provinces across mainland China. That was up from 1,100 cases reported a day earlier, and a couple hundred cases per day a week ago.

Although China suffered heavy loss of life when COVID-19 first emerged in Wuhan more than two years ago, it has had much more success than any other large country in controlling the virus since then. The surge in cases in the past few days, fueled by the omicron variant, still leaves China far below the daily case count of about 35,000 in the United States, which has less than a quarter of China’s population.