SYDNEY, Nov 12, 2014 (AFP) - Traditional Pacific island canoes sailed into Sydney Harbour on Wednesday after a journey across a vast expanse of ocean, bringing an urgent message to the world about climate change.

The leaders of three nations were onboard for a short final stretch of the epic Mua Voyage by four double-hulled canoes, which sailed from the Cook Islands via Samoa and Fiji or from New Zealand covering routes totalling more than 6,000 nautical miles.

Tommy Remengesau, the President of Palau, said the flotilla was symbolic of how Pacific Islanders had lived for thousands of years as one with nature, harnessing the power of the sun, wind and currents.

"Unfortunately our environment now is under enormous pressure from development and climate change," he said at a colourful ceremony at Sydney's Darling Harbour.

Remengesau called on the world to appreciate the value of the Pacific islands and ocean, saying that island nations needed to work with developed countries to protect the planet.

"We are all in this together, we are all in one canoe," he said.

He said the once-a-decade World Parks Congress hosted by Sydney opening Wednesday was a golden opportunity for Pacific leaders to repeat their urgings for the world to deal with climate change.

Kiribati President Anote Tong said that global warming presents an existential challenge to low-lying countries facing rising sea levels, but added it is also a wake-up call to the world.

"What we are experiencing now in our islands is just an early warning of what will happen further down the line if we do not act," he said.

"It's only a matter of time. We are the early warning system, the canaries in the coal mine."

A UN report earlier this month said under its lowest scenario global average temperatures over this century were likely to rise by 0.3-1.7 C, leading to a 26-55 centimetre sea-level rise.

Under its highest scenario, warming would be 2.6-4.8 C, causing a sea-level rise of 45-82 cm - with island nations on the frontline.

Tong spoke of a growing global momentum towards action on climate change in the lead-up to major talks in Paris later this year - saying there was a great improvement from climate talks a decade ago.

"Initially nobody listened," he said. "There was a major preoccupation with terrorism and nobody was even listening about climate change.

"I think the global community is coming around to acknowledging the reality of climate change," he said, adding: "We are running out of time."

Cook Islands Prime Minister Henry Puna agreed momentum was building.

"The challenge is to make sure they walk to talk and not just make the talk," he said.

"Not just for the Pacific Islands but for the whole world because science tells us that the Pacific ocean is the biggest absorber of carbon dioxide."

Three of the vessels in the flotilla - Marumaru Atua, Gaualofa and Uto ni Yalo - covered the journey from the Cook Islands, via Samoa, Fiji and Vanuatu while the Haunui departed from New Zealand.