A post office in Hornchurch was robbed at knifepoint.
The incident happened on Thursday (April 4) in Station Lane and officers were called at 5.25pm.
Met Police said a man entered the shop and threatened staff with a knife before leaving with a quantity of cash.
Two people sustained minor injuries during the robbery, they added.
Officers searched the area for the suspect, believed to be a white male aged between 18 to 35 years, but he was not found.
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Detectives think that the robber made off along Stanley Road and went through the alleyway leading to The Avenue.
The suspect is described as being of slim build and wearing dark clothing with black trainers that had a white sole.
At the time of the offence, the police said, he was also wearing a light-coloured woollen hat, a face mask and sunglasses.
No arrests have been made so far but enquiries continue to identify the man.
Officers have urged anyone who witnessed the incident or has dashcam/doorbell footage to call the police on 101 quoting 5614/4APR.
Information can be sent anonymously to the independent charity Crimestoppers on 0800 555 111.
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