The next time Japanese children turn up at their local park to find that their slide has disappeared overnight, they could try blaming rocketing world metal prices.

Stainless steel slides are among a growing list of metal objects to have vanished in Japan in a spate of thefts that police are blaming on rising copper prices and the insatiable appetite for scrap metal in booming China.

Last year, 5,700 such robberies were reported in locations as far apart as Shizuoka, Hiroshima and Okinawa, the national police agency said.

Thieves have made off with a bizarre array of items, including incense holders from graveyards, hundreds of metres of copper wire, and the roof of a public toilet.

Police estimate the damage is worth 2bn yen and fear that the spree is far from over, according to the Yomiuri Shimbun newspaper.

Industry insiders have been quick to point the finger at China, where the stolen metal is allegedly sold as scrap to feed a construction boom ahead of next summer's Olympics.

"Growing demand in China has created a lucrative market over there," one told the Yomiuri Shimbun newspaper.

"They don't care what kind of metal it is or where it comes from. As long as it's not too obvious that it's stolen, they'll buy it."

Police in Saitama prefecture, near Tokyo, reckon the recent theft of two children's slides under the cover of darkness was the work of a well organised gang.

"There were bolts scattered around the area, and the steps for the slides were left behind," a town official told Reuters.

"We don't know how heavy they were, but I think it must have taken at least two people to take them away."

Four similar incidents were reported last Sunday alone, including the theft of 550 kg of copper wire worth 330,000 yen in central Japan.

"With metals prices at levels where they are now, I think we will probably continue to see thefts of these kinds," said an official from the Japan Iron and Steel Recycling Institute.

"After all, you cannot have somebody guarding all public places around the clock."

Police have warned warehouse and storage yard owners to keep their premises locked at all times and to bathe them in light overnight.

In addition to depriving children of their playground fun, the thieves stand accused of sacrilege after making off with 200 stainless steel incense holders from a Buddhist cemetery in Kanagawa, where they also stole the copper roof from a public lavatory.

Ending the crime spree, though, could depend on a fall in prices rather than good detective work.

In London the price of copper has risen more than 60 percent since late 2005, when demand from China sparked a rise in prices. Japanese children will no doubt be watching the market with interest.