The area is a dedicated fan zone but is open only to key workers for first two England matches due to social distancing.
Fans arrived draped in England flags and wearing official England shirts to cheer on Gareth Southgate’s men as they start their campaign.
Mayor of London Sadiq Khan said the excitement of the Euros was needed after “the darkness and trauma” of the pandemic as he arrived at the Trafalgar Square fan zone to cheer on England in their first game against Croatia.
Mr Khan praised the “heroic” key workers, hundreds of whom have been invited to watch the game in the specially-created zone on Sunday.
“We’ve invited our amazing key workers to thank them for all they’ve done for our city,” he said.
Watch: England fans celebrate goal
“They’ve gone above and beyond over the last 18 months … this is our way to thank them.
“After the darkness and trauma of the last months we need this to uplift our spirits.
“You can tell how excited I am I’m one of the first people here … bring it home. It’ll be nice to see people face to face, facial expressions, body language.
“The best thing about football is that it brings people together.”
Addressing the England team directly, he said: “To Gareth (Southgate) and the entire England squad, London is behind you. Bring it home.”
Dr Sarah Helps, 50, a consultant clinical psychologist, said it was “brilliant” that the event had been put on for key workers.
“It’s been a phenomenally difficult few months and we’re still not out of this,” she said.
“We still need to work very hard as a nation. We need to take things slowly.
“It’s a lovely thing to do and a very nice gesture, but it doesn’t solve the need for NHS workers to have a decent pay rise and better working conditions and sufficient PPE.”
Asked about his prediction for the game, her son Thurston Gibbs, 17, said “3-1″ adding “we had better win”.
Watch: Sadiq Khan says Euro 2020 will be great and safe