NATO is set to increase the numbers of its rapid reaction force – boosting its numbers from the current 40,000 to more than 300,000.
Secretary General Jens Stoltenberg made the announcement as the military alliance is set to make clear that Russia is the "most significant and direct threat" to security when leaders from NATO nations gather in Madrid this week.
The plan being discussed in Madrid "constitutes the biggest overhaul of our collective deterrence and defence since the Cold War", Mr Stoltenberg said.
He added that the summit would be "transformative" for the alliance, with the number of troops in the alliance's high-readiness response force soaring.
The alliance would decide on a new "strategic concept for a new security reality".
Mr Stoltenberg told reporters in Brussels that it would be "a fundamental shift in NATO's deterrence and defence" and the leaders would pledge "support to Ukraine now, and for the future".
"Our new concept will guide us in an era of strategic competition."
The Secretary General added: "I expect it will make clear that allies consider Russia as the most significant and direct threat to our security."
But the plan will also address China and the "challenges that Beijing poses to our security, interests, and values".
The dramatic expansion of high-readiness forces will "strengthen our forward defences", Mr Stoltenberg said.
In response to Russia, he said "we will enhance our battlegroups in the eastern part of the alliance up to brigade-levels".
"We will transform the NATO response force and increase the number of our high-readiness forces to well over 300,000," he said.
Watch: Former Deputy Secretary General of NATO Rose Gottemoeller believes NATO are well prepared.
The NATO response force
NATO's Response Force (NRF) is a technologically advanced multinational force made up of land, air, maritime and Special Operations Forces (SOF) components that the Alliance can deploy quickly, wherever needed.
Dr Jamie Shea, former NATO Deputy Assistant Secretary General for Emerging Security Challenges described to Forces News the state of the alliance's response force.
He said: "It's a force that was set up when NATO had to go back to collected defence tasks in 2014 after Russian annexed Crimea. And NATO needed a rapid strategic reserve which could go anywhere in Europe should Russia attempt to violate NATO territory."
Mr Shea spoke about how NATO could deliver the increased numbers of force that Mr Stoltenburg proposed.
"Well, it's going to be very demanding and very challenging of course because high readiness forces are expensive."
However, he highlighted that "if you look across all the forces that NATO has, about 1.6 million, in Europe alone. You would think the allies should be able to get 300,000 of those forces in a sort of a war-fighting capable position."
Watch: Defence Secretary Ben Wallace stresses importance of British Army development.
Outlining further support for Volodymyr Zelensky's Ukraine, Mr Stoltenberg said: "Their courage and commitment are an inspiration.
"And I welcome that President Zelensky will join us at the NATO summit."
Prime Minister Boris Johnson is set to join NATO allies in Spain on Tuesday night to be a part of the talks which will set a new direction for the alliance in response to Russia's invasion of Ukraine.
The allies will agree to a strengthened comprehensive assistance package for Ukraine, with deliveries of secure communications, anti-drone systems and fuel.
The alliance will also consider Sweden and Finland's bids to join, applications made in response to the threat posed by Russia.
Turkish leader Recep Tayyip Erdogan has reservations about the plan, but he is due to hold talks with the leaders of the two countries in Madrid.
The NATO meeting follows the G7 summit in Germany which was also dominated by talks on Ukraine.