A crude, home-made bomb went off in a London train Friday morning, sending at least 22 people to the hospital. The explosion happened during rush hour, around 8:20 a.m local time. It’s been reported that none of the injuries incurred are life-threatening.The event is being labeled a terrorist attack by police.

According to the BBC’s security correspondent, Frank Gardner, the bomb — which went off at the Parsons Green station — appeared to not have properly worked. If it had, it would have killed everyone near it and caused considerably more human damage. Even so, according to witnesses, it caused a fireball that managed to engulf the train car.

“Literally within three seconds of putting your bag down, the doors just closing, we hear a loud explosion,” Charlie Craven, who said he had just boarded the train, told Reuters. “I looked around and saw this massive fireball … coming down the carriage.”

Photos and video emerging on social media showed a bucket wrapped in a reusable plastic bag from a discount supermarket called Lidl. The grocery chain released a statement shortly after the bombing saying they would support authorities in any way they could. The bomb itself appeared to be a home-made concoction of protruding wires. Video taken after the bomb went off showed the bucked still smouldering inside the train car.

“We now assess that this was a detonation of an improvised explosive device,” Assistant Commissioner Mark Rowley of the Metropolitan Police said in a statement Friday morning. “The scene remains cordoned off and the investigation continues.”

Calling it a live investigation, Rowley did not name any suspects at the time.

Photos via Reddit