Police are investigating what appears to be a deliberate fishing line booby trap tied at head-height across a Hastings bridge.

A 34-year-old motorist, who did not want to be named, was heading home when he drove into the fishing line tied across the Riverslea Road bridge at 2.30am yesterday, Hawke's Bay Today reported.

The man did not see the wire in the dark until his windscreen struck it.

"It's bloody crazy. It was right at head-height. I just hit the brakes and put my hands up and all that," he said

"If it was someone else they could have just ploughed straight into the side of the bridge. It's insane."

Motorists who arrived at the scene shook their heads at "what if" a motorcyclist or cyclist had struck the nylon strands on the 100km/h stretch - the wire could have injured or killed someone.

Senior Sergeant Luke Shadbolt said the incident was concerning and appealed for anyone who may have seen any suspicious activity in the area on Monday night to contact police.