Washington : Ten people, including a police officer, were killed in a mass shooting at a grocery store in the US state of Colorado, authorities said, adding the suspect has been apprehended. The shooting took place on Monday at the King Soopers grocery store in the city of Boulder. Addressing a press conference later in the day, Boulder Police chief Maris Herold said that the officer, identified as 51-year-old Eric Talley, was one of the first responders at the scene, Xinhua news agency reported. Herold revealed that at about 2.30 p.m., the city's police department received phone calls saying shooting incident occurred, when the crew arrived at the scene, they were shot by the suspect, who was taken into custody. She gave no more information about the shooting, saying the "complex investigation will cost at least five days" to make a conclusion. The Boulder District Attorney confirmed that an injured person was the alleged shooter and the suspect was arrested. Live video from local TV stations showed a large police presence outside the supermarket and people were escorted out of the supermarket by police officers. A shirt-less man with blood on his leg was taken out of the supermarket in handcuffs by three police officers, live TV footage showed. A law enforcement source told ABC News that officers responded to a report of someone shot in the parking area, and when they arrived at the scene, a suspect opened fire at them. CNN cited an unnamed senior law enforcement source as saying that the weapon used in the shooting was an AR-15-style rifle. Two witnesses told The Denver Post that they saw a gunman entering the store. "He just came in and started shooting," one of the witnesses was quoted as saying by the newspaper. The other witness told The Denver Post that the gunman "let off a couple of shots, then was silent, and then he let off a couple more. He wasn't spraying". "Like my fellow Coloradans, I am closely watching unfolding events in Boulder," tweeted Colorado Governor Jared Polis. "My prayers are with our fellow Coloradans in this time of sadness and grief as we learn more about the extent of the tragedy," he added. The White House confirmed that President Joe Biden has been briefed about the carnage. Before this incident, tragic mass shootings has occurred in the state. On July 20, 2012, a shooter set off tear gas grenades and shot inside a movie theatre in Aurora, killing 12 people and injuring 70 others. It was the deadliest shooting in Colorado since the Columbine High School massacre in 1999, in which two young killers murdered 12 students, a teacher and injured 21 others.