The men were arrested on suspicion of committing, preparing or instigating acts of terrorism and taken to the Metropolitan police high security custody suite in south London. On Monday night police were still searching six properties and two cars.
Two men were dragged from a car on Mansell Street, near Aldgate, east London, after it was stopped on the main road by a number of unmarked cars. The two are believed to be a 25-year-old British national of Turkish origin and a British national of Algerian origin, also 25.
A British 28-year-old of Azerbaijani origin was arrested at Westbourne Grove, west London, and another British national of Pakistani origin was arrested at a block of flats in Peckham, south-west London.
The last man was named locally as Naveed Baluch. He is thought to be from Karachi and to have attended secondary school in Walworth, south London.
The arrested men had been under MI5 surveillance for some time after intelligence was received that they were plotting attacks in Britain, according to security sources.
They are said to have been seeking to get hold of weapons to launch attacks of the kind that killed 164 people in 2008 in Mumbai, India, and last month killed at least 67 people in the Westgate shopping centre in Nairobi, Kenya.