Chinese President Xi Jinping is set to unveil a $46 billion infrastructure spending plan in Pakistan that is a centerpiece of Beijing’s ambitions to open new trade and transport routes across Asia and challenge the U.S. as the dominant regional power.

The plan, known as the China Pakistan Economic Corridor, draws on a newly expansive Chinese foreign policy and pressing economic and security concerns at home for Mr. Xi, who is expected to arrive in Pakistan on Monday. Many details had yet to be announced publicly.

“This is going to be a game-changer for Pakistan,” said Ahsan Iqbal, Pakistan’s planning minister, who said his country could link China with markets in Central Asia and South Asia.

“If we become the bridge between these three engines of growth, we will be able to carve out a large economic bloc of about 3 billion living in this part of the world…nearly half the planet.”

Beijing’s primary concern is that instability in neighboring Pakistan and Afghanistan is spilling into China’s predominantly Muslim northwest, and could grow worse with the withdrawal of U.S. troops from the region.