Four men, two armed with handguns and another with a large butcher's knife, broke into the rented property in Paddington area of the city, popular with visitors from the UAE, before threatening the tenants.
They subsequently made off with around 2,400 pounds in cash, two mobile phones, two passports, handbags and bank cards.
Three other men stood outside the property as the robbery took place today at around 1am.
The four men who raided the flat are described as black and wearing masks.
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Detective Superintendent David Manning of Westminster police said: "This is obviously a very serious incident. Although those involved were not injured they were left traumatised by their ordeal. I would appeal to anyone with any information or any witnesses to contact us as soon as possible to identify those involved."
Scotland Yard detectives are being helped by police in the UAE to try and track the robbers.
A similar smash and grab on UAE nationals at the posh Cumberland Hotel in central London earlier this month is being distanced from this incident by British police.
"It is worth noting that following the assault involving UAE nationals at the Cumberland Hotel, W1, on Sunday, 6 April, four people have been charged in connection with this. They are currently going through the judicial process," a Metropolitan police spokesperson said.