Police officers work near a property in Sunbury-on-Thames, southwest London, as part of the investigation into Friday's Parsons Green bombing, Saturday Sept, 16, 2017. British police made what they called a "significant" arrest Saturday in southern England, and searched a property in Sunbury-on-Thames as the investigaiton continues following the partially exploded bomb attack on the London subway. ( Victoria Jones/PA via AP)

Police officers work near a property in Sunbury-on-Thames, southwest London, as part of the investigation into Friday's Parsons Green bombing, Saturday Sept, 16, 2017. British police made what they called a "significant" arrest Saturday in southern England, and searched a property in Sunbury-on-Thames as the investigaiton continues following the partially exploded bomb attack on the London subway. ( Victoria Jones/PA via AP)

LONDON (AP) — The Latest on the London subway attack and manhunt for suspects (all times local):

7:50 p.m.

British police have made an apparent breakthrough in subway bombing investigation with what they are calling a “very significant” arrest, but the country remains on a “critical” alert, meaning that another attack is judged imminent.

Police arrested an 18-year-old man in the port of Dover — the main ferry link to France — and then launched a massive armed search in the southwestern London suburb of Sunbury. Residents said they were evacuated immediately as police established a huge cordon and imposed a no-fly zone above the property being searched.

Home Secretary Amber Rudd and others said the arrest was of major importance.

The man is being held under the Terrorism Act and has been brought to London for questioning. His identity is a closely guarded secret and police have implored the press not to speculate while the inquiry unfolds.

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3:50 p.m.

British Home Secretary Amber Rudd says it is “much too early” to tell if authorities knew of the suspect in the London subway bombing

Rudd said Saturday it was “good fortune” that the bomb on the District Line train did not do more damage. She said it was a “serious” improvised explosive device that could have caused much more harm.

She says the arrest Saturday of an 18-year-old suspect was “very significant” and that police are making rapid progress in the investigation. Rudd said the independent Joint Terrorism Analysis Center will gauge whether to keep the country’s terrorist threat level at “critical” in the coming days.

Rudd said she has briefed Prime Minister Theresa May on developments in the attack Friday that left 29 people injured.

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3 p.m.

British police say that armed officers are searching a home in a London suburb and evacuating neighbors as a precaution as part of the investigation into the subway blast.

Police say the operation is taking place in Sunbury, an area on the southwestern outskirts of the capital and about five miles (eight kilometers) from London’s Heathrow Airport.

Police said cordons were put in place around the neighborhood to clear the area for police.

Police earlier Saturday arrested a suspect in the port of Dover and are hoping to gather information from the suspect in custody. Police said no further arrests have been made.

A bomb partially exploded aboard a London subway train during the Friday morning rush hour, and 29 people were left injured.

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2:35 p.m.

London’s police commissioner has called on the public to be vigilant while Britain remains on high alert after a blast on a subway in the capital.

Cressida Dick says that authorities are making “some very considerable progress” in the investigation into the partial explosion of a bomb on a packed Tube train during the Friday morning rush hour. More than two dozen people were injured.

Dick said that intelligence agencies and the government are helping police “in every way they can.” She said that “London is carrying on. Carry on with your business but be alert, don’t be alarmed but make sure you tell us anything that worries you.”

Britain’s terror threat level was raised to “critical,” meaning that authorities believe an attack is imminent.

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2:05 p.m.

British officials have held an emergency Cabinet meeting to discuss the terror threat facing the country after a London subway blast injured more than two dozen people.

Home Secretary Amber Rudd chaired the Saturday session, which included ministers and senior police.

She was due to be briefed on the morning arrest of an 18-year-old man suspected of a role in the partial detonation of a device on a subway train at Parsons Green station that injured 29 people. The man was arrested in the port of Dover, where ferries link Britain and France.

Officials have left the terrorist threat level at “critical,” suggesting that other suspects in the bombing are still at large.

Hundreds of troops have been deployed at public sites throughout Britain to beef up security.

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10:45 a.m.

British police say they have arrested an 18-year-old man in connection with the London subway attack.

Police say the man has been arrested by Kent police in the port area of Dover on the English Channel.

Deputy Assistant Police Commissioner Neil Basu says that it’s a “significant arrest.” He said the investigation is ongoing and the terror threat level remains at “critical.”

The man is being held for questioning under the Terrorism Act. He has not been charged or identified.

A bomb partially exploded on a London subway train at Parsons Green station Friday morning, leaving 29 people wounded, including those with burns and injuries from an ensuing stampede.

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8:20 a.m.

London transport authorities say they have re-opened the station where a bomb partially detonated on a subway car, injuring 29 people.

The blast sent what witnesses described as a fireball through the packed train during the Friday morning rush hour. The injuries, some from the explosion and others from an ensuing stampede, where not thought to be life-threatening.

Transport for London said that the Parsons Green station in southwest London station had reopened at 1:30 a.m. on Saturday, more than 17 hours after the explosion.

British authorities increased the country’s terror threat level to “critical,” meaning they think another attack may be imminent. No arrests have been made and a major manhunt for suspects is underway. British soldiers are being deployed across the country at public sites to assist police.

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7:35 a.m.

British authorities are searching for suspects in the London subway blast that injured more than two dozen people as hundreds of soldiers are being deployed across the country.

Authorities increased the terrorism threat level to “critical” late Friday, after a bomb partially exploded during the morning rush hour, meaning a government task force believes another attack may be imminent.

The soldiers will add to the police presence Saturday at public places to deter attacks after the blast on a District Line train. No arrests have been made. The explosion and an ensuing stampede at Parsons Green station injured 29 people. None of the injuries, some of them burns, were believed to be life-threatening.

The bomb was put into a bucket and concealed in a shopping bag.