People make their way along the Long Walk towards Cambridge gate outside Windsor Castle to lay flowers for the late Queen Elizabeth II in Windsor, England, Sunday, Sept. 18, 2022. AP
Biden, accompanied by his wife Jill, crossed himself as they stood in the mediaeval hall, where the casket of Britain's longest-serving monarch has been lying in state since Wednesday.
A succession of world leaders have visited the catafalque in the oldest part of Britain's parliament.
Thousands of people made their way to Windsor Castle on Sunday, a day before the funeral of Queen Elizabeth II, to lay flowers at the gates of what will be her final resting place.
Many feared the crowds on Monday would prohibit them from paying their last respects at the palace gates, where bouquets had piled up.
Police officers were dotted along the route along the Long Walk, a 3-mile (5-kilometer) avenue where a walking funeral procession will be held before the queen is laid to rest in St. George's Chapel.
Mourners went through an security check before entering the premises. More are expected to come after the national silence is observed at 8 p.m. on Sunday. Mourners have been told not to bring tents or gazebos, only chairs and blankets. Stalls have opened along the road, selling food and refreshments.
Steve Beeson had come with his family of three and was unwrapping the plastic off his bouquet of flowers for the queen, following a strict rule by organizers.
The queen "was the only head of state we have ever known, all our lives," he said. "She has been a constant steadying of the reigns for the country through all of these really rough times, the least we can do is come and say `Thank you.'"