Melbourne: The fourth leg of the Volvo Ocean Race got under way Tuesday, with the seven boats in the gruelling round-the-world odyssey sailing from Melbourne on a tough 18-day route to Hong Kong.

The stage is a 5,800 nautical mile (10,742 kilometres) race north, up the east coast of Australia, with the navigational challenge of dodging numerous islands, before arriving in the southern Chinese city and former British territory for the first time.

“It’s going to be very tough, close racing,” said Phil Harmer, on the American-Danish yacht Vestas, which is currently running third overall.

“There is going to be someone next to you the whole way.”

Spanish team Mapfre won the third and brutal Southern Ocean stage from Cape Town to Melbourne, arriving on Christmas Eve ahead of Chinese entry Dongfeng Race Team and Vestas.

Mapfre also won the second leg from Lisbon and has the overall lead in the 11-stage race that is due to end in The Hague on June 25.

Blair Tuke, a Rio Olympic sailing gold medallist onboard Mapfre, said the crew were happy to be leading, but were realistic about what lies ahead.

“It’s a good spot to be in [first], but there’s a long, long way to go,” said Tuke, who is looking to make history by becoming the first person to win sailing’s Triple Crown of the Olympics, the America’s Cup and the Volvo.

The 2017-18 Volvo Ocean Race is the longest in the competition’s 44-year history, stretching over eight months and 45,000 nautical miles around the globe.