The 280-metre Rio Blanco had a possible leak of 2 tonnes of liquid nitrogen.
But Fire and Emergency New Zealand senior communicator Mau Barbara said the 20 firefighters and other emergency services at the scene were unable to board because of a possible Covid-19 risk on board.
"We have the problem that there is possible Covid on board so we couldn't get on board and the crews couldn't get off," Barbara said.
The entire Timaru port was evacuated.
As of 3pm today, Barbara said they had been told by the first mate of the Rio Blanco that the situation had been resolved.
"We were all ready to board the boat, PPE etc. and the first mate of the ship found what was the problem," Barbara said.
"It was a minor pressure valve leak. Because it was liquid nitrogen everything was freezing over. So as far as I know we never actually got on board the boat and the crews haven't come off the boat."
