As India readies for the United Nations to give a green light to deep sea mining and boost its economy, the environmental group Greenpeace said on Wednesday that drilling the seabed could cause irreversible harm and worsen climate change.

Without proper governance of the seas, mining could remove entire habitats and species, release toxins and create pollution in areas that have been undisturbed for millennia, it said.

"Deep sea mining could cause severe and potentially irreversible environmental harm both at the mine sites and throughout broader ocean areas," Greenpeace said in a report.

"Opening up a new industrial frontier in the largest ecosystem on Earth and undermining an important carbon sink carries significant environmental risks ... Deep sea mining could even make climate change worse."

A growing number of countries are eyeing the ocean floor as a source of wealth, scattered with vast beds of minerals key to making modern gadgets, from smartphones to solar panels.

But climate campaigners are worried about disrupting one of the last pristine areas of the planet and potentially putting species we barely understand at risk, as well as releasing planet-warming carbon dioxide.

India is investing heavily in underwater technology after winning four of 29 exploration licences awarded by the U.N's International Seabed Authority (ISA), which aims to agree rules on exploitation by 2020.

N.H. Khadge, a scientist at India's National Institute of Oceanography (NIO) that carries out sea floor surveys and tests environmental impacts of India's deep ocean exploration programme, said Greenpeace's report was "exaggerated".

He said seabed operations would be significantly less harmful than mining on land, and that environmentally-friendly technologies were being developed in line with ISA guidelines.

"It is not exploitation, it is friendly collection of the commercial deposits," he told the Thomson Reuters Foundation.

Greenpeace called on the U.N. to secure a strong Global Ocean Treaty, prioritising conservation, at talks in New York next month about oceans beyond national boundaries - an area of global governance that experts say has been neglected.

Richard Mahapatra, managing editor of India's highly-regarded Down To Earth magazine, supported Greenpeace's stance.

"In the absence of a binding global treaty, it will all be about individual interests," he said. "And that could ultimately lead to the destruction of our last frontier."