Soldiers of the People's Liberation Army prepare for a military parade marking the 70th anniversary of the founding of the People's Republic of China (PRC) at Tiananmen Square on October 1, 2019 in Beijing, China. (Photo by Han Haidan/China News Service/VCG via Getty Images)

NATO, the 29-member military alliance, was set up 70 years ago to counter the threat posed by the-then Soviet Union.

But now, another rising military power is in its sights: China.

As heads of state and government gather in the U.K. Tuesday for a two-day meeting of the alliance, shifting geopolitical relationships and emerging challenges will be in focus for the fractious group. Previous meetings have been dominated by the alliance's old foe Russia, following Moscow's annexation of Crimea from Ukraine in 2014.

However, many experts and leaders within the group think the alliance should now be focusing on new and emerging military powers, like China.

NATO Secretary General Jens Stoltenberg told delegates at the "NATO Engages" event in London, a precursor to the "Leaders Meeting" that starts Tuesday evening, that for the first time China was on NATO's agenda.

"The rise of China has security implications for all allies. There are some obvious opportunities but also some obvious challenges," he told the audience, adding that allies needed to find a "balanced way" to respond to the challenge posed by China.

Nonetheless, he said there were no plans for a "NATO-China Council," similar to the NATO-Russia Council (NRC) that was set up in 2002 to improve dialog and cooperation between NATO and Russia.

"What we see is that the rising power of China is shifting the global balance of power and the rises of China — the economic rise, the military rise — provides some opportunities but also some serious challenges," Stoltenberg told CNBC's Hadley Gamble in London.

"We have to address the fact that China is coming closer to us, investing heavily in infrastructure. We see them in Africa, we see them in the Arctic, we see them in cyber space and China now has the second-largest defense budget in the world," he said.