Columbine High School, the site of the US's deadliest school shooting eight years ago, was evacuated after a bomb threat was called in, authorities said.
No bomb was found, and no arrests were made, Jefferson County sheriff's spokeswoman Jacki Kelley said. A bomb squad, deputies and dogs searched the school and its grounds for more than three hours Thursday.
Columbine was closed for the rest of the day, and school officials said classes would resume Friday. Students were taken to a park during the evacuation, Kelley said.
Kelley said she believed more than one threat was called in to the school Thursday beginning at 9:30 a.m. She did not know whether the caller made reference to the April 20, 1999, attack by students Dylan Klebold and Eric Harris, who shot and killed 13 people before taking their own lives.