Two people have been killed after a van-ramming incident in the western German city of Muenster.
Events unfolded on social media at a slower pace than usual as police in Germany warned people not to post on Twitter and Facebook.
The driver of the vehicle died after shooting himself, police said. He is thought to be a German national and the authorities are ruling out an "Islamist" motive.
Within minutes of news breaking, Daniel Kollenberg, a student, tweeted a picture of police at the scene.
Mr Kollenberg, who witnessed the aftermath, told the BBC: "I've returned to my apartment about 300 metres from the incident site. Here I can safely watch events unfold from my window.
"I think it is a deliberate attack because it's not allowed for cars to go in this area."
He said "people are calm, but really shocked," adding that people were scared and in disbelief that such an attack could happen in Muenster.
The most used hashtag on Twitter was #Münster which was tweeted around 130,000 times on Saturday.
Paul Fegmann's was one of the most widely circulated photos on social media. It shows tables and chairs strewn outside the Grosser Kiepenkerl restaurant, which is popular with tourists.
On Facebook, people around the world expressed their solidarity for the residents of Muenster by changing their cover and profile photos.
People in Muenster used Facebook to show where queues for blood donations were happening.
Justus Ganz told the BBC: "The were 200 to 300 people of all ages in the queue.
"I'm a resident of Muenster and wanted to help in this situation.
"I live two kilometres from Kiepenkerl restaurant where it happened. In January I visited the restaurant.
"I heard about the incident when I came home from a football match because my mother was worried about us.
"All the air ambulances landed in front of her house."
Nearby Instagram users posted images of the deserted city centre.
kvdp1805 on Instagram said: "We are safe. We were about 300 yards away from the incident."
Those affected by the Sweden lorry attack exactly one year ago used social media to share their solidarity with the residents of Muenster. Margot Wallström, Minister for Foreign Affairs of Sweden, was one of these tweeters.