LOS ANGELES -- An 18-year-old male student was killed and eight others were injured in a shooting that occurred at a charter school near Denver, capital of the US western state of Colorado, on Tuesday afternoon, local police confirmed.

"It is with extreme sadness that we can confirm that 1 student at the STEM School was killed in today's #stemshooting incident. The immediate family has been notified," Douglas County Sheriff's Office tweeted about five hours after the fatal incident.

Two suspects entered the school just before 2 p.m. local time (2000 GMT) and "got deep inside the school and engaged students in two separate locations," according to Douglas County Sheriff Tony Spurlock.

"There were a number of students that were shot and injured," he said at a press briefing. He did not release the names of the victims and the suspects.

Both suspects were arrested by policemen, who arrived at the scene in 10 minutes, Spurlock said, adding that the investigators had recovered a handgun, but had no clue on the suspects' motive.

He also announced that the school has been cleared before 5 p.m. local time (2300 GMT) and investigators are no longer looking for additional suspects.

Douglas County Undersheriff Holly Nicholson-Kluth said the victims, who are all more than 15 years, had gunshot wounds and were taken to three local hospitals.

The Denver Post, a local newspaper, reported that at least four had been treated and released from hospitals by Tuesday evening.

Nicholson-Kluth briefed reporters that the officers heard gunfire as they arrived and as they entered the building, saying "quite a few shots were fired."

The incident occurred at STEM School Highlands Ranch, located about 32 km. south from downtown Denver. There are about 1,850 students in the K-12 charter school.

After hearing reports of the shooting, worried parents raced to the school to search for their children. They were redirected to a nearby recreation center to wait for reunions.

Pictures posted online showed hundreds of parents crowded at the Northridge Recreation Center in Highlands Ranch, where students from the school were taken there by buses after the fatal incident. Many parents broke into tears when they found their children.

Colorado Governor Jared Polis said in a tweet that the state is making an all-out effort to assist the Douglas County Sheriff's Department in securing the site and evacuating the students.

"We are monitoring the situation in real time. The heart of all Colorado is with the victims & their families," he tweeted.

After the shooting, US President Donald Trump's daughter, Ivanka, cancelled her scheduled Wednesday's trip to the Lockheed Martin facility in Littleton, 12 km. north of Highlands Ranch. (Xinhua)