United Nations Secretary General Ban Ki-moon said the initiative, called the Oceans Compact, sets out a strategic vision for the UN system to work more effectively to tackle the "precarious state" of the world's seas.

Ban highlighted the "grave threat" from pollution, excessive fishing and global warming.

"Our oceans are heating and expanding," he said in a speech to a conference marking the 30th anniversary of the opening for signature of the UN Convention on the Law of the Sea.

"We risk irrevocable changes in processes that we barely comprehend, such as the great currents that affect weather patterns.

"Ocean acidification (from absorbed carbon emissions) is eating into the very basis of our ocean life; and sea level rise threatens to re-draw the global map at the expense of hundreds of millions of the world's most vulnerable people."

The UN chief, who also called for action to curb piracy and irregular sea migration, said he hoped for progress towards a legally binding framework to combat "runaway climate change" at a UN conference in Doha in November.

But action could also be taken now.

Ban said the Compact aimed at "improving the health of the oceans" and strengthening their management through an action plan to be overseen by a high-level advisory group.

This would be made up of senior policymakers, scientists and ocean experts, representatives from the private sector and civil society and leaders of the UN organisations involved.