HOBART, Tasmania — Few places seem out of reach for China’s leader, Xi Jinping, who has traveled from European capitals to obscure Pacific and Caribbean islands in pursuit of his nation’s strategic interests.

So perhaps it was not surprising when he turned up last fall in this city on the edge of the Southern Ocean to put down a long-distance marker in another faraway region, Antarctica, 2,000 miles south of this Australian port.

Standing on the deck of an icebreaker that ferries Chinese scientists from this last stop before the frozen continent, Mr. Xi pledged that China would continue to expand in one of the few places on earth that remain unexploited by humans.

He signed a five-year accord with the Australian government that allows Chinese vessels and, in the future, aircraft to resupply for fuel and food before heading south. That will help secure easier access to a region that is believed to have vast oil and mineral resources; huge quantities of high-protein sea life; and for times of possible future dire need, fresh water contained in icebergs.