The incident took place after the conclusion of American singer Ariana Grande's pop concert.

Police said that they fear dozens have been injured in the attack.

Meanwhile, British Prime Minister Theresa May have postponed her campaigning for the general elections and will chair a meeting of Cobra committee later, the BBC reported.

"All our thoughts are with the victims and the families of those who have been affected," May was quoted as saying in the media.

Condemning the incident, Jeremy Corbyn, the leader of the Britain's Labour Party tweeted, "Terrible incident in Manchester. My thoughts are with all those affected and our brilliant emergency services."

Following the attack, the area was cordoned off, thereby disrupting train services.

Andy Holey, an eyewitness was quoted as saying by BBC, "As I was waiting, an explosion went off and it threw me about 30ft from one set of doors to the other set of doors."

"When I got up I saw bodies lying on the ground. My first thought was to go into the arena to try to find my family.

"When I couldn't find them, I went outside with the police and fire and looked through some of the bodies to try and find my wife and daughter," he added.

Holey eventually managed to find them in a safe state.

Some eyewitnesses have also claimed the incident as a bomb attack.

"It was definitely a bomb. It was definitely in the foyer," Emma Johnson told BBC Radio Manchester.

"The whole building shook. There was a blast and then a flash of fire afterwards. There were bodies everywhere," Emma added.

According to police, the people killed are expected to be teenagers, keeping in mind the age demography of Ariana Grande's fan following.

Grande herself tweeted that she's at a loss of words.

"broken.
from the bottom of my heart, i am so so sorry. i don't have words," her tweet read.

A similar incident had rocked Paris in November 2015, where gunmen invaded the Bataclan Concert Hall and openfired at a gig by the Eagles of Death Metal, killing at least 90 people.