CHICAGO, Jan. 25 (Xinhua) -- A strong cold front is invading U.S. Great Lakes region, sending apparent temperatures down to minus 30 degrees Celsius with a wind chill.

The U.S. National Weather Service on Friday issued a wind chill advisory for the U.S. states of Wisconsin, Illinois, Indiana, Minnesota, North Dakota and Ohio, saying a cold air mass will settle over the central and eastern United States through this weekend.

A strong cold front and arctic air mass is also expected to invade the same areas next week, producing bitterly cold wind chills and much below normal temperatures.

In Chicago, temperatures on Friday morning were recorded at minus 20 degrees Celsius, but a wind chill made it feel like 30 degrees below zero.

Cold wind chills can cause frostbite on exposed skin in as little as 30 minutes, said experts, who have advised people to wear a hat and gloves when going outside.

Six warming centers across Chicago now offer residents, especially homeless people, warming refuge from oppressive winter cold. Additional facilities are opened as needed in libraries, senior centers and other community venues, said city authorities.

In neighboring Indiana state, several dozen schools and school districts were reportedly closed due to the extremely cold weather.

Meanwhile, lake effect snow will continue to impact northeast Ohio and northwest Pennsylvania Friday afternoon, significantly reducing visibility and making travel hazardous.

Temperatures are expected to decline further as a new round of winter storm will be hitting the Great Lakes region next week, according to forecasters.