UPDATE 3.45pm: An armed police operation is under way by counter-terror officers investigating the Parsons Green bombing.
A house is being searched and residents close to the address in Sunbury-on-Thames, Surrey, are being evacuated, Scotland Yard said.
The raid comes after the arrest of an 18-year-old man in Dover earlier on Saturday who is understood to be the suspected bomber.
EARLIER: Detectives investigating the Parsons Green bombing have arrested a teenager on suspicion of a terror offence, Scotland Yard have said.
Kent Police detained the 18-year-old man in the port area of Dover on Saturday morning.
The suspect will be moved to a south London police station, the Metropolitan Police said.
Deputy Assistant Commissioner Neil Basu said: "We have made a significant arrest in our investigation this morning. Although we are pleased with the progress made, this investigation continues and the threat level remains at critical.
"The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation. We are not, at this time, changing our protective security measures and the steps taken to free up extra armed officers remain in place.
"This arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage."
The Met said 45 witnesses have been spoken to and 77 images and videos have been sent to detectives by members of the public.
A renewed appeal for information was put out by the force, asking anyone with information to call the Anti-Terrorist Hotline on 0800 789 321 or 999 in an emergency.
An improvised device detonated on a packed District Line train at Parsons Green station during the Friday morning rush hour, injuring 30.
NHS England said 19 victims were taken to hospital by ambulance, while 11 had presented themselves.
Three still remain in hospital care, the health service said.