Acting Sergeant James McDonald said about 8am last Thursday, a ute towing an unbraked tandem trailer crashed off the road 2km west of the Lindis Pass summit.
"The trailer was loaded with a 1000-litre container of chlorine," he said.
The container was damaged in the crash and over 800 litres of chlorine leaked into the road verge.
Other chemicals, including hydrochloric acid, were being transported on the back of the ute and were thrown out, but did not spill.
Acting Sgt McDonald said the driver did not have the required licences or documentation to be transporting dangerous goods.
The cause of the crash was unclear, but he confirmed alcohol was not a factor. The driver was not injured.
Charges had not been laid and investigations were ongoing, he said.
A Fenz spokesman said five crews were sent to the chemical spill from Twizel, Omarama and Otematata.
