WASHINGTON (AFP) - United States President Donald Trump's administration announced on Wednesday (Sept 11) it would soon ban flavoured e-cigarette products to stem a rising tide of youth users, following a spike in vaping-linked deaths.

The move could later be extended to an outright prohibition of vaping if adolescents migrate to tobacco flavours, seen as more legitimate products that help smokers quit their habit.

Addressing reporters at the White House, the President said that both he and First Lady Melania Trump, as parents of a teenage son, were worried about an outbreak of severe lung disease that has killed six people and sickened hundreds.

"We are both reading it," he said.

"A lot of people are reading, people are dying of vaping," he added, vowing to act.

Mr Trump was accompanied by Mr Ned Sharpless, the acting head of the Food and Drug Administration (FDA) that regulates e-cigarettes, and by Health and Human Services Secretary Alex Azar, who responded to a question about the proposed timeline by saying his agency would issue rules in the coming weeks.

Following the release of new guidance, "there will likely be about a 30-day delayed effective date", said Mr Azar. "At that point, all flavoured e-cigarettes other than tobacco flavour would have to be removed from the market."

The agency said in a release that non-tobacco flavours were being targeted for their youth appeal, with preliminary data for 2019 showing that more than a quarter of high school students had used e-cigarettes in the past 30 days.

The overwhelming majority reported using fruit, menthol or mint flavours.

While tobacco flavours will initially be exempt, manufacturers will still need to apply for FDA approval by May 2020 to continue to sell their products.

But Mr Azar also tweeted: "If data show kids migrating to tobacco-flavoured products, we will do what's necessary to tackle continued youth use of these products."

The news was a major blow to the burgeoning vaping industry, worth US$10.2 billion (S$14 billion) globally in 2018, according to Grand View Research.

MYSTERY ILLNESS

It comes amid growing concern over how more than 450 people who reported recent use of e-cigarettes have fallen ill, with initial symptoms including breathing difficulty and chest pain before some were hospitalised and placed on ventilators.

Several teens across the country have been placed in medically induced comas, including one whose doctors said may require a lung transplant if he recovers.

The Centres for Disease Control and Prevention has urged people to cease vaping while a nationwide investigation is under way.

Federal authorities have yet to identify a single substance common to all cases, but New York's health department is focusing its probe on counterfeit cannabis cartridges containing vitamin E oil, which is harmful when inhaled.

North Carolina medics have reported that patients developed acute lipoid pneumonia, a non-infectious form of the respiratory illness that occurs when oils or fat-containing substances enter the lungs.

'ILLEGAL' ADVERTISING

E-cigarettes have been available in the US since 2006 and were widely considered a safer alternative to traditional smoking, even though experts had warned even before the current wave of illnesses that it may take decades to learn about vaping's long-term effects.

While e-cigarettes do not contain the estimated 7,000 chemical constituents present in traditional cigarettes, a number of substances have been identified as potentially harmful, and the vapor could contain traces of metal, according to a 2018 study prepared for Congress.

It is also not clear why the US is so far alone in reporting such cases, and whether they are even new or only being recognised now by doctors after earlier misdiagnoses.

Whatever the case, wider public and political opinion appears to be hardening.

Mr Trump's announcement received bipartisan support, including from his long-time Republican critic and former presidential candidate Mitt Romney, and several Democrats including Senate whip Dick Durbin, who commended the FDA for "doing its job".

Billionaire and former New York mayor Michael Bloomberg, who on Tuesday announced a US$160 million campaign to ban vaping, said the flavour ban was overdue and should come into effect immediately.

The FDA has become increasingly assertive against the sector over misleading advertising and on Monday accused market-leading e-cigarette maker JUUL of breaking the law, warning it to cease presenting itself as less harmful than smoking.

But shares in Altria, which holds a one-third stake in JUUL, were stable by 4pm (4am on Thursday, Singapore time), following the announcement.