An Ashburton vandal is knocking down the region's road signs as fast as the District Council can put them up.

Almost 20 road signs have been felled in recent weeks, some by chainsaw, others by people driving into them with bull bars.

Council CEO Andrew Dalziel says at $300 a pop, the fallen signs are starting to add up.

"We're concerned with the growing cost so we're asking people to look out for that.

"We're particularly concerned about Thompson's track - just mindless stupidity."

Andrew Dalziel says the District Council are looking to prosecute the offenders.