Harry Styles is devastated by the mass shooting in Copenhagen, where he was supposed to perform just hours later.

Harry canceled his concert Sunday ... after a gunman opened fire at Field's shopping centre, which is less than 2 football fields in distance away from the venue where Harry was supposed to perform later that night.

Harry said he was feeling utter "devastation" ... "I'm heartbroken along with the people of Copenhagen. I adore this city. The people are so warm and full of love."

He went on ... "I'm devastated for the victims, their families, and everyone hurting. I'm sorry we couldn't be together. Please look after each other. H."

Police say the shooter was a 22-year-old Danish man, and they believe he acted alone. Authorities have not ruled out terrorism.

The gunman entered the mall with a rifle and then began firing randomly at people inside the mall.