More than 40 million people across the world have downloaded the global video game sensation Fortnite, but one girl in the UK has taken her love of the shoot-em-up to troubling extremes.

The nine-year-old became so obsessed with the game she wet herself rather than take a bathroom break, the Sunday People has reported.

Mum Carol said the girl, who has not been named, even hit her father in the face when her Xbox was confiscated.

Fortnite is hugely popular worldwide, with 45 million players. (Epic Games) (Fortnite)

The primary school student downloaded Fortnite after her parents bought her the console in January.

“We got called in by her head teacher asking if everything was okay. She had fallen asleep twice in lessons and her grades were slipping," Carol said.

“When we asked our daughter what the problem was, she became unusually argumentative and aggressive, which we just put down to her hormones.”

Matters came to a head when her parents noticed regular payments being made on their credit card, which turned out to be for in-game extras.

One girl in the UK is receiving treatment after becoming so obsessed with the game she wet herself rather than take a break. (Epic Games) (YouTube)

Carol and dad Richard limited their daughter's game time to one hour during the week and two hours on weekends, but their daughter was undeterred.

“My husband saw her light on in the night and found her sitting on a urine-soaked cushion playing the game," Carol said.

“I found her backside was red-raw. She was so hooked to the game she wouldn’t even go to the toilet.”

It transpired that the girl had for the past two months been waiting until her parents fell asleep and then playing Fortnite until 5am.

The girl hit her father in the face when her Xbox was confiscated. (Epic Games) (9finance)

She was ultimately sent to rehab and has been slowly recovering.

"Gaming addiction" was this year classified as a mental health condition by the World Health Organisation.

The international body's International Classification of Diseases stipulated that abnormal gaming behaviour should be evident over a period of 12 months or more before it is classed as an addiction.

Addicts display "impaired control over gaming", increasingly prioritise gaming, and increase their gaming time despite negative consequences.

Fortnite's previous peak was 3.4 million people playing concurrently. (Epic Games)

Addictions counsellor Steve Pope, who treated the nine-year-old, said he had been contacted by parents of children as young as eight about possible Fortnite addictions.

"I’ve been working in this field for three decades and never seen anything like it, how widespread and potentially damaging this is," he said.

The game in total boasts 45 million players, with about 40 million signing in every month.