A vast manhunt was launched after an improvised device partially exploded on a District Line train at Parsons Green station during the Friday morning rush hour, injuring 30. "Although we are pleased with the progress made, this investigation continues and the threat level remains at critical".
The man, who was taken into custody early Saturday morning in the town of Dover about 70 miles outside London, has not been identified by the authorities.
It comes after an 18-year-old man was arrested on Saturday at the port of Dover in connection with the blast. At least 29 passengers were injured, as several were burned and dozens attempted to escape unharmed.
Deputy Assistant Commissioner Neil Basu, the senior national coordinator for counterterrorism policing, described it as a "significant arrest" but said the investigation continues. He will be transferred to a south London police station "in due course", the statement said.
The British police added that "This arrest would lead to more activity from our officers".
Four previous attacks in London and Manchester this year claimed the lives of 35 people.
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"Our embassy officials and staff have advised the members of the Filipino community to remain calm yet vigilant even as there are no reports of Filipinos injured in the explosion", said Presidential Spokesperson Ernesto Abella.
The Manchester attack was the last time that the United Kingdom raised its threat level to critical, its highest level.
A US law enforcement source told CBS News senior investigative producer Pat Milton the device used in the attack was a white plastic bucket with a black cloth on top, with wires believed to be Christmas lights coming out of the bucket.
As of last night, detectives had spoken to 45 witnesses and were continuing to receive information from the public to the confidential anti-terrorist hotline.
British media reported that the crude device, carried in a bucket and shoved into a shopping bag, had a timer, suggesting that some degree of bombmaking knowledge was employed.