Customs officers have seized over 16,000 counterfeit ‘hoverboards’ worth an estimated $6 million.

The so-called hoverboards, which are actually two-wheeled scooters, were seized by U.S. Customs and Border Protection officers in Chicago.

 “Not only are these hoverboards a serious safety hazard but they also threaten our economic security by hurting legitimate businesses who invest significant amounts of resources into development and protection of their brands,” said U.S. Customs and Border Protection Director of Field Operations William Ferrara, in a statement released Wednesday.

Related: Citing fire concerns, NY City bans 'hoverboards' from all subways, trains and buses

The final seizure total in Chicago is expected to significantly increase in the coming weeks due to the massive amount of shipments still being processed, according to officials.

Reports continue to swirl about hoverboards catching fire.

Earlier this month the U.S. government announced that Amazon is offering refunds to customers who bought hoverboards on its website, amid ongoing safety concerns about the technology.

Related: Amazon offering 'hoverboard' refunds, government says

The U.S. Consumer Product Safety Commission (CPSC) is investigating a number of companies that make or sell hoverboards. In a statement released last week U.S. CPSC Chairman Elliot Kaye also noted that Amazon is offering hoverboard refunds.

On Wednesday New York City banned hoverboards from all subways, trains and buses, citing fire concerns.

“The safety of our customers and employees is always our top concern,” said Metropolitan Transportation Authority Chief Safety Officer David Mayer, in a statement. “For obvious reasons, it is not safe to use hoverboards, skateboards or other personal wheeled vehicles on station platforms. We’re equally concerned about the safety risk of bringing devices that pose fire hazards into the confined spaces inside trains and buses.”