Seven people died and nearly 50 were injured when a terrorist attack unfolded in the heart of the British capital on Saturday night, June 3, according to NBC News.

Officials said a vehicle barreled into pedestrians on London Bridge, and then three attackers embarked on a stabbing rampage at nearby Borough Market.

The National Health Service in England told NBC News that 21 people injured in the attack were in critical condition.

In the wake of the attack, British Prime Minister Theresa May said "things must change" when it comes to counter-terrorism policies.

London's Metropolitan Police said Sunday that they had arrested 12 people in the neighborhood of Barking and were still searching properties in the area.

Those arrested were identified by police as a 38-year-old woman, a 28-year-old man, a 52-year-old man, 55-year-old man, 27-year-old man, a 55-year-old man who has since been released without charge, 49-year-old woman, 60-year-old woman, a 19-year-old woman, a 27-year-old woman, a 24-year-old woman and a 53-year-old woman.

The incident was reported at 10:08 p.m. (5:08 p.m. ET) on Saturday. Within eight minutes, all of the suspects had been fatally shot by officers, according to authorities.

Metropolitan Police Assistant Commissioner Mark Rowley said the three men were wearing what appeared to be explosive vests but they turned out to be fake.

He added that all of the attackers were believed to have been killed but added that it was early in the investigation.

The attacks on London Bridge and at the market come two months after a driver plowed into pedestrians on Westminster Bridge in what authorities have called a terror attack, and almost two weeks after a deadly suicide bombing outside an Ariana Grande concert in Manchester.