Facebook has activated its Safety Check feature following an explosion in Manchester Arena that killed 19 people and left more than 50 injured.
The explosion occurred around 10:30pm BST (5:30 p.m. ET) as thousands of people were leaving an Ariana Grande concert.
British Prime Minister Theresa May said officials are “working to establish the full details” of the what police believe is an “appalling” terrorist attack.
Safety Check asks people in the area of the incident if they are safe, and publicly marks them as such if they say they are. Users can see which of their friends have marked themselves safe, and asks those in the area if they are.
Facebook has activated Safety Check more than 300 times in the last year, according to CNET. It was also turned on during the Westminster terror attack and after Hurricane Matthew ripped through the Caribbean, killing hundreds of people on the island of Haiti. It was first deployed in 2014.