Evidence of the potential dangers is already emerging. Toxicologists warn that e-liquids pose a significant risk to public health, particularly to children, who may be drawn to their bright colors and fragrant flavorings like cherry, chocolate and bubble gum.

“It’s not a matter of if a child will be seriously poisoned or killed,” said Lee Cantrell, director of the San Diego division of the California Poison Control System and a professor of pharmacy at the University of California, San Francisco. “It’s a matter of when.”

Reports of accidental poisonings, notably among children, are soaring. Since 2011, there appears to have been one death in the United States, a suicide by an adult who injected nicotine. But less serious cases have led to a surge in calls to poison control centers. Nationwide, the number of cases linked to e-liquids jumped to 1,351 in 2013, a 300 percent increase from 2012, and the number is on pace to double this year, according to information from the National Poison Data System. Of the cases in 2013, 365 were referred to hospitals, triple the previous year’s number.

Examples come from across the country. Last month, a 2-year-old girl in Oklahoma City drank a small bottle of a parent’s nicotine liquid, started vomiting and was rushed to an emergency room.