Investigations are underway after an incident in the Lindis Pass last Thursday, where a Queenstown contractor crashed and spilled 800 litres of chlorine onto the road verge.

Alexandra Police Acting Sergeant James McDonald said the road was closed for several hours while Fire and Emergency New Zealand (FENZ) and contractors cleaned up the chemical spill.

The driver of a Toyota Hilux, a 39-year-old man with an unbraked trailer hit a bank travelling north on the Cromwell side of the Lindis Summit.

His trailer carrying 1000L of chlorine and a separate container of hydrochloric acid on the deck of his ute both came free after the ute landed on its roof - the container of chlorine landing some 30m away.

Acting Sgt McDonald said because the driver was carrying dangerous goods, and without the required licenses to do so, it was a huge risk to emergency services at the scene.

“It could be flammable or have gas that could kill you if leaked. Some chemicals also don't mix well, so there are huge risks involved.”

Because of the seriousness of the incident, the commercial vehicle safety team was now involved while the investigation was underway to determine what charges would be laid.

“The scene was cleared and the chemicals transported back to Cromwell to a safe location,” he said.

There were also limits to how much a driver could tow with an unbraked trailer, Acting Sgt McDonald said.