Hundreds more Americans have developed a severe vaping-related illness, according to a US health official speaking at a congressional hearing on Tuesday.

The House of Representatives began public hearings this week into the mystery lung disease that, as of last week, had affected 530 people in 38 states and led to the death of nine.

“We believe that probably hundreds more [cases] have come in since the numbers we released last week,” said Dr Anne Schuchat, principal deputy director of the Centres for Disease Control and Prevention (CDC).

The outbreak prompted Massachusetts to impose a four-month ban on sales of all vaping products, including those used for tobacco and marijuana, which is legal in the state.