(CNN) Severe obesity has hit an all-time high among children in England in their last year of primary school, a government report has found.

It found that 20.2% of children measured were obese, including 4.4% who were severely obese -- that's more than 26,000 children.

The NHS defines children's obesity by calculating their Body Mass Index (BMI), taking into account their sex and age. Children above the 95th percentile are considered "obese," while children above the 99.6th percentile are considered "severely obese."

The findings come just a week after a report by the World Obesity Federation , which warned that there are 158 million obese children around the world.

According to the WOF, more than 250 million school-aged children and adolescents will be classed as obese by 2030, putting huge pressure on health care systems.

In absolute terms, the US is expected to have 17 million obese children by 2030, the largest number after China and India, the report found.

Children 'drowning in unhealthy food' options

The rate of severe obesity among children ages 10 and 11 in England marks a new record high -- and this is the fourth consecutive year the record has been broken. When the NHS first began the annual report in 2006, only 2.4% of children (numbering 10,300) in that age range were severely obese.

These findings were published on the same day that UK Chief Medical Officer Dame Sally Davies released a report urging action on solving childhood obesity. The report reiterated the government's aim of halving childhood obesity by 2030 -- a goal that "we are nowhere near achieving" in England, Davies wrote.

"Today's children are drowning in a flood of unhealthy food and drink options, compounded by insufficient opportunities for being active," she said. There are 53,000 fast food outlets in England, with 62% of them within 400 meters (1,300 feet) of a primary school, according to the report.

Obese or overweight children may experience a range of related health issues such as diabetes, asthma, depression, fatty liver disease and joint pain. Recent years have seen a rise in Type 2 diabetes among UK youth, believed to be caused by a rise in obesity.

However, Davies added that biological and social factors, like health care and ethnicity, also significantly affect which children are most vulnerable to obesity. If the wealth gap continues to widen, as many as 33% of children in the most deprived areas could be obese by 2030, she said.

This is in line with the NHS report, which found that there are twice as many obese children living in "deprived areas" than in more affluent areas. The difference in rate for severe obesity is even more extreme -- it's more than four times higher for children who live in the most deprived communities.

"Combined overweight and obesity prevalence ranged from 41.5% for children living in the most deprived areas to 24.1% for children living in the least deprived areas," the report found.

Davies called for earlier intervention in the medical sector, healthier food and drink options in the public sectors, and greater political leadership in driving change.