UPDATE: A press conference given at 10:00 p.m. ET reports that the dead stands at 19 and 59 wounded. It is believed that this has been a terrorist attack, but not confirmed and police are asking everyone to avoid the Manchester location where the attack occurred.
It has been confirmed that this was a suicide bombing as a partial body was found with a suicide vest attached to it, but police did not mention this at the press conference. (It may be due to their need to avoid sounding Islamophobic.)
No ages of the victims were given, but it is expected they are young girls and children, possibly as young as six.
U.S. Department of Homeland Security John Kelly is monitoring the attack.
DEVELOPING: An explosion outside the arena where Ariana Grande just concluded her concert has killed at least 19 and wounded about 50 people at Manchester Arena. The explosion was reported at about 10:40 p.m. local (5:40 p.m. ET).
It is probable that the bomb was a suicide attack as the wounds being seen at hospitals are shrapnel wounds.
"Ariana is okay," a representative said. "We are further investigating what happened."
It is believed the explosion did not actually occur inside the arena, but immediately outside and was detonated as people were exiting the event.
British Transport Police said that officers were posted inside the arena, which is located atop the Manchester Victoria transit station. All lines to the station were closed and Manchester cab drivers offered people free rides to their destinations.
Steve Rotheram, mayor of the Liverpool City Region, tweeted that his two daughters were at the concert and were safe. "But I fear for others," he said.
While we don't yet know the reason for the attack, my money is on radical Islamic terrorism.