President Donald Trump on Friday offered "America's friendship and partnership" to the world in his debut appearance before the global business elite in Davos, arguing: "America First does not mean America alone."

"The world is experiencing the resurgence of a strong and prosperous America. America is open for business and we are competitive once again," he added in a speech to the World Economic Forum.

Trump told his audience of politicians and leaders of industry, technology and finance that the United States was more attractive than ever to foreign investment under his year-old presidency.

But he warned: "We cannot have free and open trade if some countries exploit the system at the expense of others.

"We support free trade but it needs to be fair and it needs to be reciprocal. The United States will no longer turn a blind eye to unfair economic practices."