Police said specialist officers were assessing the suspicious package on Monday.
It comes less than 24 hours after two were taken to hospital as a precaution in a separate situation involving suspicious items found in Parliament.
Police were called into the parliamentary estate yesterday after a letter was sent to a politician, believed to be Mohammad Yasin, Labour MP for Bedford.
The spokesman later said the suspicious substances was found not to be hazardous.
According to reports, the substance deemed to be suspicious was found inside a package received by an MP's office in the building. Tests found the powder was not harmful.More news: Oclaro Inc (OCLR) Given Average Rating of "Buy" by Analysts
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A police spokesman said: "Police were called at 9.49am on Tuesday, 13 March to reports of a suspicious package at Norman Shaw Buildings, Victoria Embankment, Westminster".
A Parliament spokesman told BI in a statement that police were investigating potential links between the packages.
It is thought the package was linked to the sick "Punish a Muslim Day" after letters were sent to Muslim families in East London and the Midlands last month. "No reported injuries. Enquiries continue".
"Two people - a man and a woman - have been taken to a central London hospital as a "precaution", The Independent reports citing London's Metropolitan Police as saying".
Cops were scrambled to an incident at Westminster this morning just hours after a similar one rocked the United Kingdom government headquarters.