Fire crews battling a huge blaze on a ship in Timaru's Port have almost extinguished it entirely, a week after it broke out.

Firefighters from Timaru, Ashburton and Wellington have all been helping to bring it under control and are now due to open up the ship to fight remaining hotspots.

That comes after the Korean fishing vessel - the 80m Dong Won 701 - was boarded up over the weekend in a bid to starve the last two fires inside of oxygen.

Fire and Emergency NZ area commander Steven Greenyer said crews would continue to pump water on to the ship.

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"That will help us to keep the ship afloat and means we can use more firefighting water on board if we need it.''

The fire has been raging since last Monday, when it broke out about 9.30pm.