Police are investigating a big spike in bike thefts in central Christchurch

Over the past six weeks more than 160 bikes have been pinched - worth a total of 250 thousand dollars.

Senior Sergeant Roy Appley says cyclists should secure their bikes with a quality D-lock or similar device to deter would-be thieves.

And buyers should be wary of being offered cheap bikes, as they could be stolen.

Earlier this month five people were arrested on theft charges after a large haul of stolen bikes.