A boat made out of 12,500 recycled plastic bottles has sailed into Sydney Harbour, four months after it set out from San Francisco.

The Plastiki's journey across the Pacific Ocean was meant to raise awareness about the perils of plastic waste.

The crew of the 60-foot catamaran that weathered fierce ocean storms during its 8,000 nautical miles at sea, left San Francisco on March 20, stopping along the way at various South Pacific island nations including Kiribati and Samoa.

The boat, skippered by environmentalist David de Rothschild, a descendant of the well-known British banking family, was being towed to the Australian National Maritime Museum for a welcome ceremony.

"We hope that Sydneysiders will turn out in force to help us celebrate," de Rothschild said in a statement.

The six-member crew lived in a cabin of just 20 feet by 15 feet, took saltwater showers, and survived on a diet of dehydrated and canned food, supplemented with the occasional vegetable from their small on-board garden.

The boat is fully recyclable, and is powered in part by solar panels and windmills.

The Plastiki's name is a play on the 1947 Kon-Tiki raft sailed across the Pacific by explorer Thor Heyerdahl.

The crew briefly stopped in Queensland state last week, after battling a brutal storm off the Australian coast.

De Rothschild said the idea for the journey came to him after he read a United Nations report that said pollution and particularly plastic waste was seriously threatening the world's oceans.