Teen charged over London train bombing

An 18-year-old man has been charged with attempted murder over the London Tube terrorist attack.

London's police chief says the bomb that injured 30 on a London train could have caused more damage. (AAP)

An 18-year-old man has been charged with attempted murder and possessing explosives over the Parsons Green Tube terrorist attack in London.

Ahmed Hassan, of Sunbury, in Surrey, is accused of attempting to murder people travelling on a train in last Friday's bombing, Scotland Yard says.

He also faces a charge of using a chemical compound known as TATP to cause an explosion likely to endanger life and will appear in Westminster Magistrates Court on Friday afternoon.

Hassan was arrested Saturday at the port of Dover, a departure point for ferries to France.

Three other men remain in custody over the attack but have not been charged.

Thirty people were injured when the homemade bomb partly detonated at the height of the morning rush hour.

London police chief Cressida Dick says the bomb was packed with shrapnel and the carnage could have been much worse.