Rena salvors have detected more movement in the bow of the Rena - prompting fears it may be starting to buckle.
Maritime New Zealand spokesperson Sophie Hazelhurst said the increasing movement in the front section of the wreck possibly indicated that another piece could have given way or was beginning to buckle.
But Svitzer spokesman Matt Watson said the increasing movement did not necessarily mean it was imminently expected to give way or topple into the sea any time soon.
However, Mr Watson said since the wreck split in two the structural integrity of the vessel had been seriously compromised and had remained in a "fragile and precarious state" and continued to be closely monitored.
A Bell 214B helicopter - the world's most powerful single-engine helicopter - is being used to remove damaged containers and debris, including large chunks of timber from Bay 12, Row 12 and Bay 86 of the wreck.
Platforms for emergency winching operations to remove salvors in the event of sudden emergency have been installed.
Salvors yesterday also planned to remove two empty six-metre stock feed containers from the port side of the bow section, using the crane barge Smit Borneo.
On Sunday, 55 large bags of milk powder and cut-up containers from various bays were lifted off by helicopter on to the barge ST 60.
During Sunday's flyover, some black oil was also detected in the water and salvors planned to mop it up.
Mr Watson said the priority was to get as many containers and debris off the bow as possible.
The Smit Borneo was repositioned to near the stern of the Rena.
Various vessels continued to recover debris and containers from various locations, with 65 containers so far recovered by Braemar Howell from the water.
Ninety-nine containers had fallen overboard before the ship broke in two and an estimated 150 fell after the Rena split.
So far 463 containers have been lifted directly from the Rena for processing at Tauranga Port since the vessel grounded on Astrolabe Reef on October 5.
The debris from nine containers had also been recovered from Matakana Island, with the remains of three more to be collected.
Another successful release of little blue penguins on Sunday was reported.
Maritime New Zealand spokesperson Ross Henderson said responders remained ready to deal with any more of oil, with most clean-up operations due to resume today. The weather is forecast to be fine this week.
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