The US Embassy in London issued the alert ahead of Trump's arrival on Thursday after attending a North Atlantic Treaty Organisation summit.
After he was invited previous year, more than 1.86 million people signed a petition saying Trump should not be given a state visit because it could embarrass the queen and thousands of police will also be on duty with large protests expected.
On Tuesday, Trump left for a weeklong Europe trip that includes a meeting with Russian President Vladimir Putin in Finland and the North Atlantic Treaty Organisation summit in Brussels.
While he is in England, he will hold talks with Prime Minister Theresa May at her 16th century home, meet with Queen Elizabeth at Windsor Castle as well as attend a black-tie dinner at the former home of Winston Churchill.
The organizers continued on, "BUT people have been SO generous and supportive that we now have WAY more money than we can sensibly spend just on Trump's United Kingdom visit in July!"
Most of the protests will take place that day in central London, the US officials said, with some occurring the days before and after.
The Embassy sent a "demonstration alert" warning to citizens ahead of Donald Trump's arrival in London on Thursday July 12.
Activist Leo Murray, the man behind the blimp, said the intention is "to make sure he [Trump] knows that all of Britain is looking down on him and laughing at him".
The large gatherings "may become violent", the embassy said.
According to the Mirror, the US Embassy urged its citizens to remain vigilant during Trump's two-day visit beginning July 12, instructing Americans to "be aware of your surroundings" and watch local news for updates as the Commander-in-Chief tours the country.