Police say they have foiled an active terror plot after a woman was shot during a raid on a house in Willesden, north-west London.
The 21-year-old woman was one of the subjects of the investigation and is in a serious but stable condition.
A raid also took place in Kent, with six people arrested in total.
Officers say the operation was not connected to an arrest near Parliament on Thursday, when a man was detained on suspicion of terror offences.
The house in Harlesden Road, Willesden, which was raided on Thursday evening, had been under observation by police.
Those arrested included a 16-year-old boy, a man and woman, both aged 20 and another man and woman both aged 28. A 43-year-old woman was also arrested in Kent. All of them were detained on suspicion of the commission, preparation and instigation of terrorist acts.
The woman who was shot is under police guard in hospital but has not been arrested "due to her condition",
Alex Paton, 50, who lives in Harlesden Road, said he saw a woman "getting all cuffed up and put in a white suit".
He described seeing "coppers and masked men with guns".
Another resident said she had heard the "bang, bang, bang" of shots.
A neighbour of the raided property suggested the shot woman had suffered injuries to her left arm and stomach.
He said the family who lived there were from Somalia.
'Don't touch me'
Ruth Haile, who lives in the road, said she heard shots and the woman on the ground shouting: "Don't touch me, my body, don't touch my dress."
It is believed to be the first time a woman has been shot by police in 10 years. The last time was in 2007 when Ann Sanderson was fatally shot in Kent.
Police said searches had taken place at "linked addresses", as well as where the arrests took place.
Neil Basu, deputy assistant commissioner of the Metropolitan Police, said: "Due to these arrests that have been made yesterday, in both cases I believe that we have contained the threats that they pose."
How serious is it?
By home affairs correspondent Dominic Casciani
The intelligence convinced Scotland Yard they needed to go in fast and hard to carry out arrests.
That means they feared there was some kind of threat that needed to be contained - a threat that required a large team of the most highly-trained available officers.
They fired CS gas canisters into the building, smashing holes in the top front window.
The 21-year-old woman who was shot is not one of those under arrest - but has been described by police as one of the "subjects" - security services speak for someone at the heart of an operation.
We don't know anything about how and why she was injured and that will be subject of a police watchdog investigation, as is always the case.
The Willesden raid has been referred to the Independent Police Complaints Commission and the Met's directorate of professional standards, as is procedure.
The IPCC said it was gathering evidence but that no officers were under investigation.
On Thursday, police arrested a 27-year-old man at the junction of Parliament Street and Parliament Square, in London, as part of an intelligence-led operation.
He was identified on Friday as Khalid Mohamed Omar Ali, a British national who is believed to have gone to school in Tottenham, north London, but was not born in the UK.
The Met said he had been detained on suspicion of terrorism offences and that knives were recovered from the scene.
He had been on the force's radar for some time and it is thought police acted after a concerned family member contacted them.
Home Secretary Amber Rudd said she had spoken to the Met about both incidents and thanked them for their actions.
"I would like to reinforce my gratitude to the police and security services, who work tirelessly around the clock to keep the people of this country safe," she said.
"They carry out their duties with calmness and professionalism, and we are all grateful for their dedication."