LONDON: The 17-year-old boy was detained after officers executed a warrant at an address in Thornton Heath, south London, at around 12.05am on Thursday.
All six remain in custody at a south London police station, Scotland Yard said.
Meanwhile officers have begun a search of the property where the teenager was arrested under section 41 of the Terrorism Act.
Commander Dean Haydon, head of the Met’s Counter Terrorism Command, said: “This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday.
“We now have six males in custody and searches are continuing at five addresses. Detectives are carrying out extensive inquiries to determine the full facts behind the attack.”
The investigation into the rush hour bombing – which injured 30 people – has seen three men aged 25, 30 and 48, detained in Newport, south Wales, a 21-year-old named Yahyah Farroukh arrested in Hounslow, west London, and an 18-year-old man detained at the Port of Dover.
A time limit on Mr Farroukh’s detention is expected to expire today, while detectives have been given until Saturday to continue questioning the 18-year-old suspect.
Police tape is in place around a house in Thornton Heath and a man in a forensic suit went in. A police car was parked outside and officers were standing guard.
Neighbours on Saint Paul’s Road said they believed the property was a halfway house, and one said there has been trouble at that house before. Phil Burt, 67, who has lived at the opposite side of the street for 40 years, said he heard “enormous shouts” at around midnight.
“We had trouble with that house in the past. I’m not surprised to see tape around there. I think at one stage it was used as an in between house.
“I think they tried to use it for ex-jail people and I think they tried to use it for asylum seekers.”
He said the shouting, which he is not sure whether it came from the police or not, was so loud that it made at least three dogs in the area bark. Speaking about trouble at the house in the past, he said: “At one stage there were drug pushers in there.”
He also said he thinks there was some police activity at the house “maybe a month ago”.
Paula Anderson, 43, lives next door to the property and said she was also woken up by “a lot of banging”, adding: “When I looked out there were lots of police officers.”
She said her husband went out and asked the police about what was going on and they told him they were “acting on intelligence”. She said she has never had any problems with living next door to the house, which she said probably has about seven or eight bedrooms.
A woman who lives a few doors down, and did not want to be named, said the property was a halfway house and usually occupied by young people.
“All we know is that they’d come and they’d go, they come and they go,” she said.
The woman said it has been a halfway house for the seven years she has lived in the area.
— Metropolitan Police (@metpoliceuk) September 21, 2017