Metropolitan Police officers were called to Dean House on Dean Street in the city's West End district of Soho following a report that the duo had entered and demanded money.
"They threatened staff and tied up one male employee before leaving the scene in an unknown direction with an amount of money and mobile phones.
"No one was injured during the incident, however, one man has been treated for shock. No shots were fired," a Scotland Yard statement said.
The suspects have been described as speaking with Eastern European accents and were wearing white hooded jackets.
