China's research icebreaker Xuelong-2, carrying out the country's 40th Antarctic expedition, rendezvoused with supply vessel Tianhui in waters off the South Island of New Zealand, as the two ships started to pass through the westerlies on Saturday en route to Antarctica.

The expedition team set sail on November 1, on a mission expected to last over five months.

The westerlies are prevailing winds that form in the middle latitudes between 40 and 60 degrees and can reach 6 to 7 on the Beaufort scale generating four- to five-meter ocean swells throughout the year.

Crossing through the westerlies is one of the many challenges facing Antarctic expeditions, and crews aboard the expedition ships prepared for it by lashing down equipment, including a helicopter, to the decks of their ships.

The cargo vessel Tianhui is carrying construction materials weighing about 9,300 tonnes for China's new Antarctic research station, including steel components, modules, curtain wall panels, and some sand and gravel materials, said Zheng Di, deputy team leader of the Ross Sea scientific research station.

To ensure safe passage of the two ships through the westerlies, ship captains and other expedition leaders worked together to chart the optimal route.

"Based on the meteorological forecasts we have collected, we conducted a comprehensive assessment, and overall it is manageable. Our current plan is to navigate below the area with swells reaching four meters whenever possible," said Xiao Zhimin, captain of Xuelong-2.