It is being called the biggest attack in France since World War II.
On Nov. 13, two suicide bombers detonated themselves outside a soccer stadium, while gunmen in a shooting rampage stormed through restaurants and bars before entering the Bataclan concert hall where an American rock band was playing.
By the time police came in, the attackers had already detonated their explosives, also killing many around them. The overall death toll is currently more than 150.
As authorities are still trying to make sense of what happened, French President Francois Hollande declared a state of emergency.
Amid the tension, Facebook was one of the first online networks to offer help by activating the Facebook Safety Check feature. Friends and family could check if their loved ones were hurt in the shootings and blasts.
The Twitter community also came together with the creation of the hashtag #PorteOuverte, which means "open door."
As Paris police were evacuating the streets surrounding the stadium and concert hall, concerned citizens were using the hashtag to indicate that they were opening up their homes as a safe haven for anyone caught in the chaos.
Within just a few hours, at least 400,000 Tweets using the safety hashtag were posted and a new Twitter account called @PorteOuverteFRA was created specifically to retweet the addresses and phone numbers of volunteers opening up their doors as safe places for the night.
— Sarah (@lemaldelinfini) November 14, 2015
I have room for stranded people near chatelet. Tell me if you're in need, #PorteOuverte. — Arnaud Dupuis (@ArnaudDupuis) November 14, 2015
Some taxis were also reportedly offering their services for free to bring dozens of people to safety after the attack.
Taxis within Paris are offering free journeys to homes and hotels. Be sure to use these services if you are stuck in the city #PorteOuverte
— #PorteOuverte (@PorteOuverteFRA) November 14, 2015
The hashtag is also being used in the U.S. by Americans willing to open up their homes to those who are #StrandedInUS due to the cancellation of flights to France.
Or #PorteOuverte. I can accommodate 3 comfortably & have some good wine here in #Chicago near the @cta Blue Line. https://t.co/1S6n6RtM6c — Chris Cwiak (@ChrisCwiak) November 14, 2015