Authorities in the US city of Chicago have issued a new mask mandate that required everyone over the age of two to wear masks when indoors.

In a statement issued on Friday, the Chicago Department of Public Health recommended that “businesses, employers, and event organizers require universal masking in all public indoor settings”, reports Xinhua news agency.

The new guidance keeps masks outdoors optional and makes no changes to the recommendations for social distancing.

“We are taking this step to prevent further spread of the very contagious Delta variant and to protect public health,” said Allison Arwady, the city’s public health commissioner, in the statement.

“This isn’t forever, but it is necessary to help decrease the risk for all Chicagoans right now.”

Cook County was added on Thursday to the Centers for Disease Control and Prevention (CDC) list of areas experiencing “substantial” Covid-19 transmission.

Cook, DuPage, McHenry and Will counties in the Chicago area, and 80 others across the state of Illinois have all met the threshold where masks are recommended for everyone indoors, regardless of vaccination status.

The CDC announced the new guidelines Tuesday for counties experiencing “substantial” or “high” transmission, as the Delta variant of COVID-19 surged across the country.

The office of the Illinois Secretary of State announced on Tuesday to re-institute mask policy in all Driver Services facilities, Secretary of State offices and the Illinois State Capitol Building starting from August 2.

Illinois Governor J.B. Pritzker ordered on Thursday that masks be worn at all state facilities under his control.

Illinois health officials on Friday reported 2,348 new Covid-19 cases, the second time in three days the tally topped 2,000.

Over the past seven days, the state averaged 1,669 new daily cases, up roughly 46 per cent from the previous week’s average of 1,140 cases per day.

Illinois recorded a peak of 3,390 daily cases in mid-April during the spring surge.

Along with new Covid-19 cases, hospitalizations are also on the rise in Illinois.

Currently, 903 people were hospitalised statewide with Covid-19, bringing the seven-day average to 796, the highest level since the week ending June 9, when the state was averaging 816 Covid-19 patients each day.