(Reuters) - A woman was critically injured in a shooting inside a downtown Denver office building on Tuesday and police said the suspected gunman was pronounced dead at the scene with what appeared to be a self-inflicted gunshot wound.

Denver Police spokesman Doug Schepman told reporters at a news conference that the woman was shot multiple times around 2:45 p.m. local time (2045 GMT) and was taken to a hospital in critical condition.

The suspect appeared to specifically target the victim, Schepman said, adding that the building was searched and secured and no further threats were found. He said he did not know what type of weapon was used in the shooting.

Police said streets in the vicinity were closed and that although the scene was secure, the investigation was ongoing.

The Denver Post newspaper uploaded video online showing office workers with their hands above their heads fleeing the building dubbed the Alliance Center, a hub for environmental activism groups and other organizations.

Jacob Smith, a programs director for the Alliance for Sustainable Colorado, referred questions about the shooting to Denver police when reached by email.

Diana Best, a Greenpeace worker who went to the center to meet with someone from another environmental group, told the Denver Post: "I heard screaming, I saw the door to the second floor open and there was just loud screaming."

"It seems like it's out of control. I'm still shaking. As a human being, we have to figure out what to do with gun violence," she added, according to the newspaper.

Earlier this month, a gunman opened fire inside a gay nightclub in Orlando, killing 49 people and injuring another 53, in the deadliest mass shooting in modern U.S. history.

(Reporting by Curtis Skinner in San Francisco; editing by James Dalgleish, G Crosse)