A chemical company will face the full force of the law if it's found to have covered up the release of cyanide into Gladstone harbour, the Premier says.

Authorities are investigating Orica Australia after it admitted releasing waste water with double the allowed level of cyanide into the central Queensland harbour.

The Department of Environment and Resource Management (DERM) said the releases happened in January and February and the company was now the subject of a full investigation.

The probe includes tests to determine any environmental effects and whether Orica breached a requirement to immediately report the matter to authorities.

"Certainly it is very serious when a company doesn't observe the requirements under its environmental authority and report these incidences immediately to the regulator," DERM associate director-general Terry Wall said.