A rescue operation to save the crew of a Russian fishing boat sinking in the icy Antarctic waters is expected to take up to five days, New Zealand shipping authorities said Friday.

The Sparta had begun unloading some of its crew and cargo on to the ice after it started taking on water deep in the Southern Ocean, according to Maritime New Zealand (MNZ).

Two other fishing vessels were making their way to the Sparta, but were not expected to reach the area for four to five days, said a statement from MNZ.

The Sparta, with 32 crew aboard 15 Russians, 16 Indonesian and one Ukrainian issued a distress call from a position next to the Antarctic ice shelf in the Ross Sea at about 3 a.m. New Zealand time.

The 55-meter vessel was about 2,000 nautical miles (3,704 kilometers) southeast of New Zealand, according to MNZ.

The Rescue Coordination Centre New Zealand (RCCNZ) had confirmed the ship was taking on water and currently had a 13- degree list.

All of the crew were understood to be safe, and they were pumping water out of the holds and discharging cargo on to the ice to lighten the ship.

"Some of the crew have been offloaded onto the ice, as a precautionary measure," said the statement.

RCCNZ search and rescue mission coordinator Ramon Davis said RCCNZ had contacted a number of vessels operating in the southern ocean, but heavy sea ice was making vessel movement difficult.

Sparta's sister ship, Chiyo Maru no. 3, was making its way towards the stricken vessel, but was about 290 nautical miles away and had no capacity to cut or break through sea ice.

The New Zealand vessel, San Aspiring, which had some capacity to move through ice, was also making its way towards Sparta, and was currently 470 nautical miles away.

At its current speed, it was expected to reach the vessel in four to five days, said the statement.

The RCCNZ was continuing to contact vessels in the Southern Ocean to see if there were any others with ice capability that could assist.

The weather in the area currently was calm and about 3 degrees Centigrade.

Sparta issued a distress call via Inmarsat-C, a satellite communications system, which was picked up by the Norwegian rescue coordination centre and passed on to the RCCNZ. Initial efforts to contact Sparta directly were unsuccessful.

Around 4.20 a.m. Sparta's sister ship, Chiyo Maru no. 3, relayed a Mayday call to RCCNZ, and confirmed Sparta was taking on water.