CHICAGO (AP) — Public health officials in Chicago are warning of a second wave of COVID-19 cases, with a more than 50% increase of positive cases to over 500 per day.

Chicago Mayor Lori Lightfoot says the city is considering additional restrictions. Department of Public Health Commissioner Allison Arwady says it is the most cases since late May, which was the end of the coronavirus pandemic’s first wave.

She says the increases are across all groups of Chicagoans and parts of the city. There’s also been an increase in hospitalizations. Lightfoot is stressing the importance of masks, even in small gatherings.