UNITED NATIONS, United States (AFP) - UN member states on Saturday agreed to begin negotiations on a treaty to protect marine biodiversity in ocean areas extending beyond territorial waters, in a move heralded by environmental organisations.

By calling to preserve vast areas threatened by pollution, overfishing and global warming, the eventual UN treaty would be the first to specifically address protection of marine life.

But the agreement was reached only after a small group of countries engaged in fishing and ocean mining blocked a more rapid timeline during the discussions between experts from the 193 member countries.

A majority of nations called for quick action but several countries such as the United States, Russia, Canada, Iceland and Japan expressed reluctance.

The agreement was welcomed by the High Seas Alliance made up of 27 NGOs plus the International Union for the Conservation of Nature, which called it "a major step toward urgently needed ocean protection."

"This is a big moment for the high seas," said Karen Sack of the Pew Charitable Trusts, calling it "really good news for life in the global ocean."

The treaty represents international zones that make up 64 per cent of the world's oceans or a total of 43 per cent of Earth's surface.

"Today's agreement could go a long way in securing the protection the high seas desperately need," Greenpeace's Sofia Tsenikli said in a statement.

The agreement was made after four days of discussions in New York, and the outcome of the meeting must still be adopted by the UN General Assembly by September.

International treaties and conventions already regulate activities such as fishing or protection of certain areas, but no text covers all dangers threatening marine life.

The UN has been in discussions for 10 years, but the General Assembly pushed for action following the Rio+20 conference on Earth's environmental problems and enduring poverty in 2012.