Supporters of vaping say the devices are a far healthier alternative to smoking tobacco and can help smokers to kick the habit. But many health experts dispute their claims and remain sceptical about the supposed benefits of e-cigarettes.

Sex Party MP Fiona Patten, who spoke at the rally in support of vaping, said the new legislation needed to be reviewed. The new law also bans the sale of e-cigarettes to children.

"Let's protect children but let's protect adults by allowing them to vapourise," she said.

Beneath clouds of sickly sweet vapour the protesters rallied for their right to use electronic devices that mimic the experience of smoking. They carried placards that said "vaping saves lives" and "bullied for smoking bullied for quitting".

University of NSW Associate Professor Colin Mendelsohn​, who attended the rally, said vaping was an effective and safe way to help smokers quit.

"It's a unique technology that works much better than other treatments," he said.

But Sydney University public health Emeritus Professor Simon Chapman cited American research from the Centers for Disease Control and Prevention that showed the use of e-cigarettes increased substantially among students in grades six to eight in 2014/15. Those devices may have contained a nicotine-based liquid.

Professor Chapman said vaping was almost certainly less dangerous than smoking.

"That's because almost anything is safer than cigarettes. They are the Mount Everest of danger," he said.

Too little was known about the possible health problems that e-cigarettes may cause, Professor Chapman said. "Given we don't know what the long-term consequences are going to be, it is a concern."

He said major tobacco companies had entered the e-cigarette market in some countries overseas.

The Victorian chiefs of Quit, Australian Medical Association, Heart Foundation and Cancer Council have written to Victorian MPs in support of regulating e-cigarettes.

The new law places restrictions on advertising e-cigarettes. And bans on displaying and selling tobacco will also apply to e-cigarettes or vapes.

It is currently illegal to sell e-cigarettes that contain nicotine although some users bypass the law by buying nicotine liquid from overseas.

The letter from the health groups said the new laws would not prevent e-cigarettes from being used as a quitting aid in future if the Therapeutic Goods Administration found they were safe and effective.

The groups also support the ban on vaping in smoke-free areas, saying it is in line with community expectations.

The letter cited Cancer Council Victoria data showing that curiosity was the most common reason for Victorians to use e-cigarettes.

But Paul McNamara, who owns two vaping product stores, said the new laws would make it impossible to properly demonstrate the e-cigarette devices in his shops. He said the government was making it "as hard as possible" for smokers to give up cigarettes.