Environment Canterbury's worried swells may delay the rescue of a fishing boat beached off the coast of Canterbury's Shell Bay.
The vessel, which ran aground on Sunday, had about 10,000 litres of diesel and 400 litres of hydraulic oil onboard.
Images show the vessel on rocks, spilling oil near an endangered penguin colony.
Environment Canterbury Commander Emma Parr says crews are battling two metre swells and king tides - which are forecast to worsen.
"We are concerned for those wildlife, they are high risk and sensitive. We're preparing for an oiled wildlife response."
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