“The Foreign Office has been liaising with their counterparts in France,” Theresa May’s spokesman said. “We are ready to assist if required.”
Official travel advice urges British visitors to Paris to “exercise caution, avoid the affected area and follow the advice of local authorities” due to the continuing threat.
Police union official Yves Lefebvre said the man was carrying two backpacks and two machetes, and launched an attack when soldiers told the man he could not enter with his bags.
An American tourist visiting Le Louvre described how sirens sounded before emergency escape doors lifted from the ground.
“Four armed guards then sprinted around the grounds outside of the pyramid entrance looking for something,” he wrote on Twitter.
Another man, Olivier Majewski, was leaving his scooter in the parking area beneath Le Louvre when he saw a crush of around 30 people running and screaming “there’s been a terror attack”.
The 53-year-old said he hid for about 15 minutes before making his way upstairs. He said people were clearly scared, adding: “They were panicked.”
French police secure the site near the Louvre Pyramid in Paris (Reuters)
Hundreds of people were evacuated from Le Louvre art gallery, Carrousel du Loure shopping centre, nearby Palais Royal metro station and surrounding gardens.
Around 250 people inside the museum were being held in “safe areas” by police, who moved tourists away from windows and pulled down the shutters as operations continued.
They have since been evacuated area has been reopened to the public, with surrounding roadblocks lifted.
It came following a series of Isis-inspired terror attacks in France, with the group calling on its followers to attack “infidels” and members of the security services.
The group massacred 130 people in a series of shootings and bombings in November 2015, and its followers have killed shoppers at a Kosher supermarket, a police officer and his wife and a Catholic priest.
More than 3,500 soldiers are currently patrolling Paris as part of increased security measures under the ongoing state of emergency, which has sparked human rights concerns.
Continued attacks and rising support for the far right Front National party has put pressure on Mr Hollande’s government ahead of France’s national elections.