Firefighters are continuing to battle blazes on a ship in Timaru Harbour that have been burning for five days.

Crews have been fighting the fire on Korean fishing vesel Dong Won 701 since it broke out about 9pm on Monday and will continue to monitor it overnight and over the weekend using a thermal imaging camera.

The fire is yet to be fully extinguished and may not be until Monday next week. Two fires - one in the cargo hold and another at the front of the boat - are still burning.

Today about about 20 firefighters had been working to starve the blazes of oxygen by sealing up portholes and gaps.

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Steven Greenyer, Fire and Emergency New Zealand's area manager for South Canterbury, said this had been effective and the fires were only smouldering now.

"We're hopeful that we're getting on top of it, and while it's still smoldering, come Monday we hope the fire will be completely out."