Biden, on his first foreign trip as president, flew in from Britain, where he attended a G7 summit, and was welcomed by Belgian Prime Minister Alexander De Croo.

After a handshake and a brief exchange of words, he got into the armoured limousine known as "The Beast" to head for the US embassy in Brussels, his base during his stay there.

Brussels has launched a major security operation to ensure the safety of Biden and the leaders of the 28 other NATO members states arriving for the summit. Brussels residents have been warned to expect disruption to their normal routines.

The summit is expected to see Biden mark a resumption of the US's leading role in NATO after the disruption of the Trump presidency.

After a three-hour meeting Monday afternoon, NATO leaders are due to launch a joint statement.

They are hoping to formulate a tough message for Vladimir Putin to give Biden something substantial to take to Geneva for his summit with the Russian president on Wednesday.

The NATO summit is also likely to security issues in space, cyberspace, and the growing influence of China.