A cowboy builder who spilt concrete down a stormwater drain on Auckland's North Shore could face prosecution.

More than half a cubic metre of concrete was spilled on to the road, left to run down a kerb and into down a stormwater drain in Torbay on Wednesday.

The incident happened on Glenvar Rd shortly after 10.30am.

A member of the public alerted Auckland Council to the sticky situation, and a "suck truck" was promptly sent to the scene to siphon the concrete out of the drain.

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A "suck truck" was promptly sent to the scene to siphon the concrete out of the drain. Photo / Supplied

Contractors arrived in the nick of time to remove the concrete before it set.

Auckland Council has tracked down the person behind the mess, and an investigation is under way.

A prosecution could follow, although no decision has yet been made on further action.

Auckland Council's Healthy Waters Operations team manager Frank Tian said the concrete could have caused "serious issues" had it hardened before it was found.

"Our contractors reacted very quickly and the concrete was still soft when they arrived," he said.

"But if no one had reported this to council, or they had reported it a few hours later, it would have been like rock."

The incident happened on Glenvar Rd, in Torbay on Wednesday. Photo / Google
The incident happened on Glenvar Rd, in Torbay on Wednesday. Photo / Google

Tian said the main cause for concern was rain.

"Luckily, the weather was quite good when this happened," he said.

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If it began to rain after the concrete had hardened, water would have built up and the drain would have flooded.

If a downpour had set in when the concrete was still soft, it could have flushed it down into streams or open water where it could kill fish or other marine wildlife.

In similar instances in the past, Tian said, the concrete had made its way into streams where it had caused the death of several eels.

Other times, it had hardened and blocked drainage pipes. In those cases council contractors had to break the ground and replace the pipe to remove the blockage.

Tian said this type of incident was not common.