Police in Hong Kong are investigating an elaborate device found embedded in the turf at the Happy Valley racetrack apparently designed to shoot poison darts at the animals at the start of a race.

A track supervisor unearthed the device on Wednesday morning while making routine checks of the starting points for races scheduled that evening at the track, the Hong Kong Jockey Club said in a statement.

The remote-controlled shooter included 12 metal tubes, each a foot long, filled with darts buried in the grass under the spot where the starting gates would be situated for 1,200 metre (3,937ft) races on Wednesday night.

The tubes, spaced so each would aim up at a horse, were wired together and linked to a wireless receiver, according to a local newspaper and a police source. "The obvious intent was that it was going to fire these little darts which have got some kind of chemical in it . . . up from the ground up to where the horse's starting gate is," said the senior police source.

"I doubt very much that it was meant to do anything more than just slightly tranquillize the horse. That's my speculation."

The police source said the shooter was almost certainly related to betting, and could be linked to organised crime syndicates, known as triads.

"It could well be that triads are part of that, especially the gambling which is done outside the Jockey Club's system," he said. "If you can get the horse to slow down just enough, it looks like a normal race and the favourite may not come in." The darts had been sent to a laboratory to try to identify the chemical used.