A second man in connection to Friday’s terrorist attack in London has been arrested, British police said.

The attack which occurred at Parsons Green has left 30 people injured when a homemade bomb exploded during peak hour.

The 21-year-old man was arrested in the suburb of Hounslow in London's west last night, the Metropolitan Police force said in a statement.

Detained under Britain’s Terrorism Act, he was then taken to a south London police station, the force added.

Earlier on Saturday, police detained an 18-year-old man in the city of Dover – the main ferry link to France. The police also attacked a property in Sunbury, a small town outside London, as they hunted for the terrorists.

Hounslow is located six kilometers from Sunbury, where police launched an investigation in connection with the attack.

The bomb which was in a bucket within a shopping back, exploded about 8:20am local time on Friday.

ISIS claimed responsibility for the terror attack saying one of its units planted the bomb on the train.

British authorities believe another attack is imminent.

British Prime Minister Teresa May said raising the threat level to its highest point was a “proportionate and sensible step.”

In recent years, ISIS has carried out several attacks in some European countries, including France and Britain.