Greater Manchester Police in the U.K. warned the public to avoid the area around Manchester Arena Monday night after people attending an Ariana Grande concert reported hearing an explosion of some sort.

One person described the sound of a “weird bang” immediately as the lights came up after the show, although some described it as a series of gunshots and others an explosion.

Update:

NBC News is reporting that at least 20 are dead and hundreds more injured, although police have not issued any public statement on the number of fatalities.

Update:

People say 19 fatalities have been confirmed.

Update:

Police held an early-morning news conference that confirmed the basics: 19 were killed in what appears to have been a terrorist attack.

Twitchy will update this post as details become available.