Armed officers were sent to Derry Street, where Sony's offices are located, after police were alerted at around 11:00 am (1100 GMT), London's Metropolitan Police said in a statement.
British media reported that the incident occurred in the Sony Music building.
Double stabbing at Amsterdam station in possible terror attack
"Evacuations have taken place as a precaution," police said.
Police said emergency medical workers were in attendance.
The area is in the High Street Kensington shopping district and Sony Music is opposite the offices of the Daily Mail newspaper.
Trish Ellis, a personal assistant at The Mail on Sunday newspaper who witnessed the incident, told the Press Association news agency: "Armed police were going in six-plus at a time, and more and more of them but they seemed to be keeping people in the building.
"Gradually they started to release people in tens, twenties," she said.
COMMENTS (1)
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ