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Hospital admissions where obesity is a factor have more than doubled in England during the last four years, new figures from NHS Digital suggest.

There were almost 617,000 appointments in 2016-17 where obesity was either a primary or secondary diagnosis - up from 292,000 in 2012-13.

Primary diagnoses involve weight-loss treatment, while secondary ones include hip problems and heart attacks.

Public Health England said it showed obesity was a "significant challenge".

Obesity is linked to a range of health problems, including heart disease, diabetes and cancer.

A secondary diagnosis of obesity means it would not be the reason for the admission but a factor that may contribute to the health issue and affect the type of care a patient receives.

Obesity was the main cause of 10,705 admissions - an 8% increase on the year before - and bariatric surgery appointments increased by 5% to 6,760 over the same period.

Those aged between 35 and 64 made up 69% of the admissions.

Women accounted for 66% of all obesity-related appointments and 77% of bariatric surgeries.

Image copyright Getty Images Image caption The report also found a growing obesity divide between children living in the poorest and richest areas

NHS Digital's annual study also highlighted a growing obesity divide between children living in the poorest and richest areas.

The gap in the percentage of these children who are obese at reception age has increased from 4.5 to 6.8% since 2007-8.

But the gap among year six children has grown by more, from 8.5% to 15%.

The report also found:

Wirral, Southampton and Slough had the highest admission rates, while Telford and Wrekin and Redcar & Cleveland had the highest rates of obesity related bariatric surgery

25% of women and 21% of men were classed as inactive in 2016

Just 16% of children consumed the recommended five portions of fruit and vegetables a day in 2016 - down from 23% in 2014

But the proportion of children meeting government physical activity guidelines rose - from 21% in 2012 to 23% in 2015 for boys, and from 16% in 2012 to 20% in 2015 for girls

'Public health crisis'

The Royal College of Paediatrics and Child Health said the figures showed the "urgency" that was needed to tackle obesity in childhood.

Its president, Prof Russell Viner, said: "We know that obese children are likely to go on to be obese in adulthood, which can result in serious conditions such as type 2 diabetes and cardiovascular disease.

"The increase in hospital admissions directly attributed to obesity is an indicator that this impact is already being seen."

Professor Louis Levy, head of nutrition science for Public Health England, said the figures showed obesity remained a "significant challenge" across England.

"It's taken many years for levels of obesity to reach this point and change will not happen overnight," he said.

Professor Jonathan Valabhji, national clinical director for diabetes and obesity at NHS England, said: "We have been clear that the growing obesity crisis sweeping the country is a public health crisis and the evidence backs it up.

"Our own sugar restrictions, the new sugar tax and the NHS diabetes prevention programme are all part of what needs to be a concerted effort to address obesity."

NHS Digital said it was possible that some of the increase in obesity-related admissions may be down to better recording of obesity by doctors on patient notes.

The government's sugar tax on sweetened drinks will come into effect on Friday.