Thousands of demonstrators marched through central London on Wednesday afternoon to protest against U.S. President Donald Trump's second state visit to Britain, as Trump was being feted at Windsor Castle by the royal family.

Protesters waved placards criticizing U.S. policies on immigration, Gaza and climate change, marching to the sound of trumpets and drums from Portland Place to Parliament Square.

U.S. citizen Amanda said that she traveled to London from Los Angeles just for the protest. "I think everything is just very messed up right now. We don't have good leadership and I'm very worried for the direction that the United States is taking and the world," she said.

The British government said Tuesday that Britain and the United States agreed on a multi-billion-dollar tech deal during Trump's visit to boost fast-growing fields such as AI, quantum computing and nuclear, noting that Google will open a data center in Waltham Cross, Hertfordshire.

Philip Threlfall, a resident from Hitchin, a town in Hertfordshire, told Xinhua that building such a center is "inevitable," but "they are gonna be a bad thing for everybody, just gonna eat power, eat up wetland and produce the same old rubbish multi-times over."

Metropolitan Police said Wednesday that they estimated up to 5,000 people were in attendance. They also announced Tuesday that more than 1,600 officers would be deployed for the large demonstration and warned the event must conclude by 7 p.m. local time.

The demonstration was organized by the "Stop Trump Coalition" group, who also led a protest in Windsor on Tuesday evening with nearly 100 residents from Windsor and other parts of Britain gathering before Trump's arrival.

According to Buckingham Palace, Trump and British Prime Minister Keir Starmer are scheduled to hold a bilateral meeting on Thursday, the last day of his visit, at Chequers, the prime minister's country residence.