(Bloomberg) –– President Donald Trump called vaping a “problem” and his health secretary said the government would force companies to remove flavored vaping products from the market after reports of hundreds of U.S. cases of a mysterious illness related to e-cigarette devices.

“Not only is it a problem overall, but really specifically with respect for children,” Trump told reporters at the White House after a meeting with advisers including Health and Human Services Secretary Alex Azar and Acting Food and Drug Administration Commissioner Norman Sharpless.

“We may very well have to do something very, very strong about it,” Trump said.

Azar said the FDA would soon issue regulatory guidance allowing the agency to remove flavored vaping products that are believed to appeal to children. Five million children are using e-cigarette products, Azar said, calling it an “alarming” trend.

More than 450 cases of the respiratory condition were reported as of Sept. 6, according to the Centers for Disease Control and Prevention. The severity of the cases vary, but six people have died.

Around the country, doctors have now seen hundreds of cases where patients — often youthful, previously healthy adults — have shown up in the emergency room, suddenly stricken with dangerous respiratory damage.

The U.S. Centers for Disease Control and Prevention has said anyone who uses a vape device should consider stopping while public health officials investigate the cause of the condition. The CDC said on Friday that the lung-injury cases were appearing most often in people who used vaping products containing THC, the key psychoactive ingredient in cannabis.

State health officials in New York have pointed to vitamin E acetate as a likely culprit. While thought to be harmless when used as a nutritional supplement, it could carry risks when inhaled and has been found in some products, said New York health officials.

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