More teenagers are becoming addicted to the internet with an estimated 930,000 junior high and high school students nationwide overusing online services, a health ministry team said Friday.

The figure is double the number from the previous survey in 2013, and showed that more female students were hooked than males. The team said the prevalence of smartphone games and social networking services is partly to blame for the surge.

Internet addicts can become reclusive or violent toward family members and might be at risk of neurological problems and illnesses such as depression.

The survey by the Health, Labor and Welfare Ministry was conducted between December and February and targeted students at 103 junior high and high schools in Japan. Some 64,000 students responded.

It showed 10.6 percent of junior high school boys and 14.3 percent of junior high school girls were using the internet obsessively. Among high school students, 13.2 percent of boys and 18.9 percent of girls were doing the same.

Students were deemed to be obsessive users if at least five of eight statements indicative of internet addiction applied to their behavior. This included a statement that said: “You go into a sulk if you are going to stop using the internet.”

The 930,000 estimate produced by the latest study is up from the 510,000 seen in 2013.

Excessive playing of online games has become a global issue, prompting the World Health Organization to add gaming disorder to its list of medical conditions in June.

Last year a 22-year-old man in China’s Zhejiang Province was reportedly rushed to the hospital after playing online games for four days in a row, without eating or drinking, and coming down with a kidney disorder.

The Chinese government said Thursday it plans to control the release of online games to prevent young people from becoming near-sighted.

In South Korea a man in his 20s who frequented an internet cafe starved his 2-year-old son by leaving him at home in 2014, while another man in his 20s died after playing games online for 86 hours virtually without sleep in 2002.

The South Korean government is taking steps to fight the problem by introducing treatment programs.