Fire and Emergency New Zealand's area manager for South Canterbury, Steven Greenyer, says the fire has been contained but there is still some steam and smoke coming from the ship.
"It's still not fully extinguished, but it's looking a lot better than it was about four to five hours ago. We're reasonably confident it's not going to escalate," he said.
Greenyer said two more crews are on their way from Christchurch and a further two will come from Dunedin to help relieve those who have been working overnight.
"Both paid and volunteer firefighters have been working incredibly hard to get this fire under control, in some pretty trying conditions. The weather overnight has been appalling, it's been very wet and cold."
He said firefighters have had to be careful with the amount of water they use on the blaze to avoid the boat sinking.
The police have cordoned off part of the Port area as a precaution.