The Health Minister is dismissing calls from dozens of public health specialists to urgently introduce a 20 percent tax on sugary drinks.

A group of more than 70 public health experts has written an open letter to Cabinet, asking for stronger obesity prevention measures to fight childhood obesity.

A recent report published in The Lancet showed New Zealand had one of the highest numbers of overweight people in the world.

The researchers' letter described the strategies presented last year by the government to fight obesity as 'soft'.

They said they wanted a 20 percent excise tax on sugary drinks, which they expected would raise between $30m and $40m.

But Health Minister Jonathan Coleman said there was no proof a tax would work and the government was keeping 'a watching brief' on emerging research, including from the University of Waikato and University of North Carolina.

Dr Coleman said Denmark had revoked their tax on sugary drinks, and if a tax was implemented in New Zealand there could be 'substitution effects with people drinking different types of beverages'.

New Zealand had a comprehensive anti-obesity package with 22 initiatives to combat the issue, he said.

The open letter included damning criticism of the Food and Grocery Council, who were accused of putting forward arguments aimed at creating 'doubt in the public's mind and spook(ing) politicians into inaction'.

Food and Grocery Council chief executive Katherine Rich said some of the criticism 'bordered on hysteria'.

Ms Rich said her own research of Mexico's two-year old tax on sugary drinks revealed while consumption dropped in 2014, the following year it bounced back.

"What we've used is gold-standard data from Nielsen and put out there information that clearly shows in black and white that certainly in Mexico the sugar tax has not been a success."

One of the letter's signatories, Professor Boyd Swinburn of Auckland University, said any study funded by the sugary drinks industry needed to be scrutinised.

It was natural the council would oppose the move because it was aimed at reducing products its members made and it would employ the same tactics as the tobacco and alcohol industries had to prevent a tax, he said.