DENVER — A man carrying a gun and declaring “I am the emperor” was shot and killed Monday outside the offices of the Colorado governor, Bill Ritter, by a security officer, a spokesman said. Mr. Ritter was not injured.

The unidentified man refused orders to drop his gun, a spokesman, Evan Dreyer, said. Four or five shots were heard, but authorities would not say how many times the security officer fired.

Before he was shot, the gunman said, “I am the emperor and I’m here to take over state government,” Mr. Dreyer said.

The shooting occurred in a hall outside the governor’s offices on the first floor of the Capitol. Mr. Dreyer said Mr. Ritter was in the Capitol at the time but would not say where.

“The governor is fine,” Mr. Dreyer said. “Everybody is a bit rattled.”

The Capitol has no metal detectors. They are usually installed temporarily during the governor’s annual State of the State address in January but then are removed.

State Rep. Edward Casso said he saw the gunman after the shooting and described him as being in his 30s or 40s, dressed in a white shirt and dark slacks.

Mr. Casso said a state patrolman told him to evacuate, adding, “I started to panic a little bit. I was just hoping that was the end of it.”

Authorities roped off the area where the man was shot, and an ambulance and eight police cars converged on the building’s north entrance.

Pat Garriott said he was eating in the basement cafeteria when he heard shots.

“We heard a series of loud bangs, about four,” he said. “My partner and I looked up and saw a flash of smoke. We figured out it was probably gunshots.”

Security agents rushed them into a basement office for safety and kept them there for about 20 minutes, he said.

Mr. Casso, a first-term Democrat, said the Capitol should have metal detectors.

“It’s kind of freaky someone could get that close,” he said.