Virtual loot boxes bought in video games with real cash for a chance to get in-game goodies may not technically be considered gambling.
But they can be as addictive as gambling, said social workers and video game experts.
Senior counsellor Andrea Chan recalled how one 12-year-old client at Touch Youth Intervention spent $3,000 on in-game purchases in one week. Most of the money went to buying loot boxes, she said.
In another case, a student struck a deal with his parents - scoring well for the examinations meant the student would get $1,000 to spend on loot box games.
"Games with loot boxes that affect game play mean that gamers are 'compelled' to keep trying to use the loot boxes... to win something to progress," Ms Chan said.
"The young merely view the game as fun without understanding potential consequences."
Many loot boxes often burst open with much fanfare, including sound effects and attractive animations. But critics point out that loot box mechanics are similar to gambling and warn that they can be addictive.
"Slot machines at casinos also come with such sensory triggers and that is not a coincidence," said Mr Brian Russman, deputy chief clinical officer at The Cabin Addiction Services Group. He believes that loot box mechanics are not strictly considered gambling, although they are "definitely on the line".
Dr Thomas Lee, addiction specialist at Resilienz Clinic, added that part of the addictiveness of loot boxes comes from not knowing what one might get.
"If there is a fixed outcome, you lose interest after a while," he explained. "But if there's is no fixed outcome, you are more likely to continue... The unpredictability provides a thrill and excitement."
In fact, such game mechanics stimulate the production of a biochemical known as dopamine, which is linked to rewards and motivation, said Mr Michael David Thompson, lecturer at DigiPen Singapore's game software design and production facility.
This can make loot boxes very addictive, Mr Thompson said. "If you then add a financial cost to influencing the outcome of the set of actions, you're putting those who are prone to gambling addiction at risk," he added.
However, Dr Munidasa Winslow, psychiatrist at Winslow Clinic, pointed out that such marketing tactics are often seen to some degree in the real world as well.
Online stores selling clothes or beauty products sometimes hold mystery box promotions. Many trading card game companies also sell cards in sealed booster packs.
"You never know what's inside the packet, but for the chance of getting a good card you are willing to put down money," he said.
Dr Winslow, who plays computer games himself, said he does not feel that loot boxes are any more of a concern than other tactics that game companies use to get people to spend money.
These can include encouraging players to buy items that make it easier to defeat an enemy, or getting them to form alliances and rely on peer pressure to help drive up in-game purchases.
Instead, what is important is educating parents and children to be aware of such subtle marketing tactics, he said. "It's less obvious in cyberspace, because everything there is bright and shiny."
Ms Chan also pointed out that virtual loot boxes are more easily accessible than their physical counterparts. "As everything is digitised and gamified, the barrier to click and spend for a chance to get good loot is lowered... Players sometimes do not feel like they are spending real money," she said.
Ms Chan said that parents should also take note of the values that such games may be imparting to children. She said: "By allowing them to play a game which allows them to pay for a random chance to get a prize to help them advance... our children may end up learning that luck is more important than hard work."
•Additional reporting by Lester Hio