A 16-year-old Cambodian kick-boxer died after being smacked in the head by his opponent, officials said on Thursday, raising concerns about young boys being forced into the wildly popular, but dangerous, sport.

Chhu Thon was knocked down on Monday by a 14-year-old opponent in a 30,000-riel ($7.5) bout at a Buddhist temple in Banteay Meanchey, a remote jungle-clad province in northwest Cambodia. He died shortly afterwards.

"He was hit really hard," local police chief Chhit Seng told Reuters. "We think he died of concussion."

Cambodian kick-boxing -- almost identical to the Thai variety -- is hugely popular in the impoverished southeast Asian nation, which claims to have invented the no-holds-barred sport centuries ago.

Prizes are meagre by Western standards, but the ring represents a route out of the gutter for youngsters. A shot at local superstardom is not without its risks, however.

At least two other boxers have been killed since 1996, and in the near-total absence of medical facilities or regulation, doctors are concerned more and more young boys are being forced to risk their lives as prize fighters.

"We worry when we see kids being trained to be boxers because they are vulnerable to being killed. The teenage body is not yet strong enough," said Chhoeung Yavyen, official doctor of the Cambodian Amateur Boxing Federation.