Salvage crews working on the ill-fated MV Rena have finally removed containers from the front section of the stricken ship for the first time, but the stench from rotting contents on-board has made it more challenging for the team, according to reports.

Rena, which split in half over severe weather 12 days ago, is now emitting a pungent smell, spreading for kilometres over the area, as the contents of its containers still on board begin to rot, according to ONE News reporter Kim Vinnell.

Various items were loaded into the containers, such as cow hides and food, among others.

Maritime New Zealand said the Rena's bow position on the Astrolabe Reef off the Tauranga coast means the crane barge Smit Borneo cannot get close enough to the port side to lift off some containers, reports TVNZ.

Salvors reported 10 containers have been lifted off the Rena since the vessel split in two pieces, but over 500 remain missing while divers are still studying how to best locate the others.

Marine authorities are now considering remote controlled submarines to assess the seabed, TVNZ reports, as some containers could still be on Rena's sunken stern.

Salvage unit manager Kenny Crawford told TVNZ the gases are monitored all the time for the safety of the salvors.

The waters are presently calm in the Bay of Plenty, where that Rena got stuck on a reef causing a major oil spill over three months ago, before it broke in pieces due to heavy water swells. But divers are hampered by sea surges and jagged steel.

Rena's initial major spill leaked about 360 tonnes of oil and small amounts of oil continue to leak from the vessel.

Crawford also told TVNZ tests are being carried out on the toxicity of water to ensure the safety of salvors.