Council workers were rushed out of Kensington Town Hall this morning due to a bomb threat.
Met Police officers raced to the scene shortly before 10am and told those inside to evacuate.
The building has since been declared safe and people were able to go inside a little after 10.30am.
A member of staff, who declined to be named, told the Standard: "I was in the building and the police came in the the building and they said there was a security alert and we had to evacuate."
He said they had "no idea" when they were rushed out what the issue was.
Workers were evacuated from the west London building, in Hornton Street, while its customer service centre was also closed along with Kensington Central Library.
Royal Borough of Kensington and Chelsea was previously unable to take calls due to the incident.
A Kensington and Chelsea Council spokesman said: "Kensington Town Hall, including the Customer Service Centre, and Kensington Library, have now reopened. At around 9:30am today all staff were evacuated from the Town Hall and the police were called following a bomb threat.
“The police investigated and confirmed the building was safe shortly before 11am. All staff have returned to work and all services are successfully up and running."
A spokesman for the Metropolitan Police earlier said the force had been called to reports of a suspicious package.
They later added their action at the Town Hall had been "stood down" after the building was searched and nothing was found.
There was to be no further investigation into the incident, Scotland Yard said.
