This is the dramatic moment a hero security guard leapt into a swimming pool to save a drowning child.

Wicharn Charoensat, 49, was on duty at a housing estate guardhouse when he was told that a boy was drowning at a pool club in Pathum Thani, central Thailand, on Saturday.

CCTV footage shows the brave officer plunging into the 10ft deep pool to save Arnon Taengnim, 15, who was seen motionless at the bottom.

Arnon's friends threw life preservers into the water as the guard dragged the unconscious schoolboy toward the edge. Staff performed CPR 'for a long time' until the boy began breathing again.

Paramedics later arrived and found the teen alive but with a very faint pulse. He was rushed to the Pathum Thani Hospital where he remains in a critical condition.

The hero security officer said: 'I was stationed at the booth in front of the housing estate when it happened. There were a lot of adults at the pool, but no one leapt in to help. A group of older boys tried, but they couldn't do anything. The boy had been underwater too long, and the water was just too deep.'

Arnon's friend Wanmai, 13, said it was the first time Arnon had come swimming with them. She said: 'I asked him if he knew how to swim and he said he did. At around 1 pm, he jumped into the pool and started paddling to the other side. But not long after, he looked like he was drowning.

'At first, we thought he was just playing around because he's always such a prankster. We didn't think much of it until he kept his hand raised for a long time. That's when we realised he was really in trouble.'

Security cameras captured Arnon's struggle as he was seen flailing his arms trying to propel himself to safety.

His grandmother Sulee Kongkakoon, 54, who had been taking care of Arnon since his parents separated, said the teen was still unconscious and had a '50/50 chance of survival'.

Doctors said his blood pressure was low and his pupils were not fully responding to light.

Sulee said: 'That day, Arnon called me to ask for money and permission to go swimming with his friends. He assured me he could swim, so I told him to take care of himself and transferred the money at around 12:50 pm. I found out what happened not long after, since I live nearby in a government housing complex.'

She said pool management offered to cover her travel and leave expenses as she watches over Arnon in the hospital.

She said: 'I was angry at them for not having lifeguards at the pool. Though the kids are grown enough to look after themselves, there should have been someone there to oversee their safety.'

The grandmother added that she was now 'desperately hoping for a miracle' to save her beloved grandson, the eldest of three siblings and a straight-A student enrolled on an academic scholarship.