An oil spill at Timaru Port that was discovered at midday is now being cleaned up by members of the Environment Canterbury oil response team.
The amount of oil leaked is reported to be between 40 and 50 litres and the spilled substance is believed to be light fuel oil.
Environment Canterbury Regional Harbourmaster Jim Dilley said the current focus was on containment and cleaning up the oil.
"Once that is done, we will then launch an investigation, but right now our priority is to lessen the impact on the environment as much as possible."
He would not reveal the name of the boat the leak is understood to have come from.