The museum was evacuated and the area was cordoned off with police tape, while reports said there were helicopters above and emergency services at the scene.
Mark added: 'I think everyone seems to be just trying to carry on as normal because no one knows what is happening'.
A man arrested following a crash outside London's Natural History Museum has been released under investigation, police said.
In a statement, the Met said: "Whilst enquiries continue it is believed a auto mounted the pavement and collided with a number of pedestrians".
Paramedics treated 11 people, primarily for leg and head injuries, and transported nine of them to the hospital, according to a statement from Peter McKenna, deputy director of operations for London Ambulance Service.
Eleven people were hurt in the collision although none of their injuries are believed to be life threatening or life changing.
A spokesman said the incident, which unfolded around 2:20 p.m. local time, was not being treated as terrorism-related at this stage.
London Mayor Sadiq Khan also tweeted his thanks and hopes for a "swift recovery" for those injured.
A man is restrained on the ground at the scene.
What happened: A auto mounted the sidewalk near the South Kensington museum at around 2:20 p.m. local time, hitting several pedestrians.
Witness footage appeared to show a man being held on the ground by three others following the collision.
Police have launched an inquiry to trace the motive behind the incident.
Downing Street said the Prime Minister was being kept up-to-date on developments.
Police said they are working to establish the circumstances of the crash and more information will be provided once details are clear.
Britain has been on a "severe" terrorist threat level indicating that the Joint Terrorism Analysis Center believes an attack is viewed as highly likely. So far no casualties have been reported and the metropolitan police are investigating the case. In March, a terrorist rammed his vehicle into the side of the Parliament building in the British capital killing four people.