THE shipwreck Rena has finally sunk. Salvagers are struggling to recover more than 400 containers from the wild New Zealand seas.

The operation suffered a major setback yesterday when the rear section of the boat sank, taking all its heavy cargo with it.

Just a small section of the stern remains poking up through the waves, with the rest now resting on the Astrolabe Reef.

"With hundreds of these containers now underwater we have a very different, even more challenging situation to deal with," Svitzer Salvage spokesman Matthew Watson said.

The operation is in observation-only mode until the wreck appears to settle.

Meanwhile, more than 150 containers adrift since the weekend have floated north, 25 of which washed ashore.

Read more on the Herald Sun.