Whizboard Store manager "Mor Loud" demonstrates the Hoverboard on Broadway in Times Square in New York, Dec. 15, 2015. Getty Images

Amid investigations into the safety of hoverboards because of reports that some burst into flame, U.S. Customs and Border Protection on Wednesday announced Chicago is the site of the highest number of unsafe hoverboards seized to date, about 16,000 in total, WGN-TV in Chicago reported. Authorities said the popular two-wheeled toys, much of them shipped to Chicago from East Asia or China, could have caught fire or even exploded.

Customs and Border Protection began to notice unsafe hoverboards were coming into the U.S. in air shipments and ocean containers earlier this month. Officials said the hoverboards collected, worth about $10 million, don’t pass U.S. safety regulations.

Some of the boards had fake trademarks to trick customers, and the batteries in the toys were potentially dangerous. There have been more than three-dozen documented instances of the toys catching fire during battery-charging, leading to growing safety concerns and retailers pulling them off shelves and websites, the Daily Mail reported.

The hoverboard fires haven’t been confined to the boards themselves — in some cases the fires started with the toys and led to whole houses being engulfed in flames. The toys gained significant popularity during the recent holiday season.

Since early December, border agents have seized unsafe counterfeit hoverboards in Miami and near the Canadian borders with New York and Minnesota, but in much smaller amounts, various media outlets reported.

The U.S. is not the only country known to confiscate unsafe hoverboards. Between October and December, the United Kingdom seized about 15,000 boards coming into the country that were deemed not safe, CNBC reported.

Concerns over hoverboard safety have even left the government of the Australian state of Victoria to consider a ban on the toy, the Guardian reported. The call for the ban came after a house in Australia burned to the ground because a hoverboard exploded.