Donald Trump has been labelled a "shit" on Twitter by a user who is believed to be a student at the Florida school where 17 students were shot dead.
The reply by "Sarah" to the US president's public comment on the mass killing went viral after she urged him to introduce gun control measures instead of platitudes.
Mr Trump had tweeted his "prayers and condolences" to the families of the dead, adding: "No child, teacher or anyone else should ever feel unsafe in an American school.
My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school.— Donald J. Trump (@realDonaldTrump) February 14, 2018
The account @chaddiedabaddie, which says it belongs to the girl attending Marjory Stoneman Douglas High School in Parkland, near Fort Lauderdale, replied: "I don't want your condolences you f****** price (sic) of shit, my friends and teachers were shot.
"Multiple of my fellow classmates are dead. Do something instead of sending prayers.
"Prayers won't fix this. But Gun control will prevent it from happening again.
By Thursday morning her message had been retweeted 65,000 times and liked by more than 154,000 people.
She had earlier tweeted: "Today has been the worst day of my life. I've been crying helplessly for hours. Thank you to everyone for your support. I'm going to try to sleep now."
Today has been the worst day of my life. I’ve been crying helplessly for hours. Thank you to everyone for your support. I’m going to try to sleep now. #DouglasStrong— Sarah Chadwick (@Sarahchadwickk) February 15, 2018
The suspected gunman, named as 19-year-old Nikolas Cruz, was arrested after heavily armed police swarmed into the school.
It was reported that Cruz was a former student who had been expelled.
Another student who was in class at the time of the shooting said she "cannot unsee" the terror that unfolded before her.
Morgan Williams described on Twitter how her friends were killed as the gunman roamed through the school corridors.
She said: "I cannot stop hearing the sound of the gun as he walked down my hallway. I cannot unsee my classmates who were shot get carried out by police. I cannot unsee the bodies on the floor. Please keep in mind the horror of what we've gone through today. #prayfordouglas"
I cannot stop hearing the sound of the gun as he walked down my hallway. I cannot unsee my classmates who were shot get carried out by police. I cannot unsee the bodies on the floor. Please keep in mind the horror of what we’ve gone through today. #prayfordouglas— Morgan Williams (@morganw_44) February 15, 2018
She added: "Never in a million years did I think I would have EVER gone through this. There is NO reason why I should have had to run past deceased friends and classmates to get to safety because there isn't a control on how easy it is to get a gun."
Other students posted social media footage of the siege under way.
One user, Aidan Minoff, appeared to be taking shelter under tables alongside his school mates.
He wrote on Twitter: "My school is being shot up and I am locked inside. I'm f****** scared right now"
The original tweet, posted by Sarah, was seized upon by several high-profile names in the entertainment industry.
Josh Gad, who became known as the voice of Olaf in Disney's blockbuster Frozen, wrote on Twitter: "Retweet this until you are blue in the face."
Ali A Rizvi, a Pakistani-Canadian author best known for The Atheist Muslim, said simply: "Message to Donald Trump from a Douglas High School student. #Parkland #Guncontrol"