Image copyright Getty Images Image caption A trend in which Vietnamese teenagers have been doing stunts for likes has gone viral on Facebook, with dangerous results

A social media trend promising dangerous stunts in exchange for Facebook likes is causing alarm in Vietnam, and concerns about cyber bullying, as Pham Lan Phuong of BBC Vietnamese explains.

How far would you go for a million Facebook likes?

For one young man in Ho Chi Minh City, the answer is serious injury, possibly death. He has promised to jump off the fourth floor of a tower block if that many people "like" his pledge to do so.

The incident is just one of many linked to a viral trend of #vietnamnoilalam, or "Young Vietnamese will deliver what they promise".

Image copyright Facebook Image caption The original post of the man who called for 40,000 likes in order for him to self-immolate

The trend appears to have been started by the man pledging to jump, who the BBC is not naming.

In September, he promised to set fire to himself if he got 40,000 likes. He exceeded his target.

As a result, hundreds of young teenagers flocked to a canal in Ho Chi Minh City to see him perform the act.

Image copyright Facebook Image caption Hundreds of people gathered to watch the man who announced that he would set himself on fire

Viral videos later showed the man, in his 20s, setting fire to his coat and immediately jumping into the water.

Days later, the same man later promised to stab himself, getting 88,000 likes immediately after the announcement.

He posted a video showing that he had stabbed himself in the arm with a knife. He gained 79,000 followers from the incidents.

Image copyright Facebook Image caption The man who stabbed himself in the arm with a knife could be a victim of digital bullies

Then in early October, a 13-year-old girl posted that she would "burn the school" if she reached 1,000 likes. She reached that within two days.

In a clip posted on Facebook, which went viral, she was seen sprinkling gasoline on the gate and chairs in front of a room at a school.

A crowd watching her immediately dispersed as fire caught on to her legs. She suffered burns to her legs and was later treated at the local hospital.

The case is still being investigated by police, while the school principal told media outlets he had advised students not to post such statuses, and taught them how to use Facebook properly.

Police official Do Canh Thin, deputy director of the Centre of Research and Criminology Investigation, called this phenomenon an "unhealthy trend", saying it could lead to "deviant, delusion and folly".

"This phenomenon is concerning," he told Dan Tri newspaper.

"Such actions to find fame at any price have spread so dramatically amongst young teenagers. A lack of action could push them into crime and felony if there is no effective way to stop them."

'Not jokes anymore'

Not all the dares are potentially life-threatening.

Image copyright Facebook Image caption In another case, a young girl posted that she would run naked around a university campus if she got 7,000 likes

Student Nguyen Ngoc Kim Thu said she saw one man promising to dress up as a woman, and another daring to ride a motorbike naked after he reached 1,000 likes.

"There is nothing serious here, just a kind of online challenge, like the Ice Bucket Challenge some years ago, I thought," she said.

"My friends also shared similar statuses and we liked and we waited to see if anything happened. There is nothing serious at all, that guy did not burn himself. He just wants to be famous."

But sociology student Dang Tien Tai, told the BBC the dares were "not jokes anymore".

"I am frightened by the idea of burning a house, a school," he said.

"They are making scary things become true, that is terrible. What if they got more and more likes, just to harm their bodies, their lives?"

'Trapped' into trouble

Dang Thanh Hang, a masters fellow of Contemporary East Asian Studies at the University of Duisburg Essen, told the BBC that posting and completing a dare was "a quick ego boost in a virtual space".

But he said that after posting the requests "they quickly become a victim of digital bullies".

The girl who set fire to the school, for example, later told news outlet Dat Viet Online that she had been threatened into carrying out the act.

Some people had "bought gasoline and forced her", she said, or she would be beaten.

"If they decide to back off, they will not only 'lose face' but also face violent threats.

"They would have no other choice but to perform the act. In some sense, they are the victims, trapped in their own requests for trouble."

Since his first dare, the man behind the trend has continued to challenge people on Facebook to make danger pledges, and received many videos in response.

Within 24 hours of posting, more than 35,000 people had already "liked" his pledge to jump.

So far there have been no deaths from the dangerous stunts. But there is increasing pressure on the authorities to intervene, before a dare goes too far.