MELBOURNE, Australia (AP) — Australia and Papua New Guinea’s prime ministers on Tuesday began trekking into the South Pacific island nation’s mountainous interior to commemorate a pivotal World War II campaign and to underscore their current security alliance, which faces challenges from China’s growing regional influence.

Australian Prime Minister Anthony Albanese received an elaborate traditional welcome when he arrived by helicopter at Kokoda Village with his Papua New Guinean counterpart James Marape.

The pair will walk 15 kilometers (9 miles) over two days along the rugged Kokoda Track where the Japanese army’s advance toward what is now the national capital, Port Moresby, was halted in 1942 in the wilds of the Owen Stanley Range.

“In forging a relationship of brothers and sisters, together as one we will go forward,” Albanese told Australian Broadcasting Corp. as the pair set off from the village in tropical heat and humidity.