More children will be overweight than underweight by 2022, if global trends continue, World Health Organization experts say.

WHO's warning came in Tuesday's publication of a study, undertaken in conjunction with Imperial College London, which measured the weight and height of almost 130 million people above the age of five worldwide.

It is the largest ever study of its kind.

The report's findings "highlight, remind and reinforce that overweight and obesity is a global health crisis today, and threatens to worsen in coming years unless we start taking drastic action", said Dr Fiona Bull, a programme coordinator for the WHO.

The nearly 200 million children classified as moderately or severely underweight also continue to pose a major public health challenge, the report's authors said.

Rates of obesity among those aged 5-19 have increased tenfold in just over four decades, from 11 million in 1975 to 124 million in 2016.

Lead author of the report, Majid Ezzati, professor at Imperial's School of Public Health, said: "Over the past four decades, obesity rates in children and adolescents have soared globally, and continue to do so in low and middle-income countries."

Children more vulnerable

Children are now more likely to be overweight than not in a number of middle-income countries, including in regions such as East Asia, Latin America and the Caribbean.

This may be a result of increased consumption of highly processed and energy-dense foods, the report's authors said.

Such foods are known to cause weight gain and other health issues when eaten in excess.

"These worrying trends reflect the impact of food marketing and policies across the globe, with healthy nutritious foods too expensive for poor families and communities," Ezzati said.

"We need ways to make healthy, nutritious food more available at home and school, especially in poor families and communities, and regulations and taxes to protect children from unhealthy foods."

Obesity rates have stabilised in high-income countries in recent years, though levels remain unacceptably high, Ezzati added.

Almost two billion people worldwide are now overweight, 671 million of which are obese, the study revealed.