Two Houston bike patrol officers subdued a gunman who was pointing and shooting a rifle in downtown's Tranquillity Park near the Occupy Houston encampment late Monday afternoon, bringing moments of terror to an otherwise routine rush hour.

Despite hails of gunfire from both law enforcement and the rifle-waving man, no bystanders or officers were injured.

The 21-year-old man was struck at least twice and taken to Ben Taub General Hospital with injuries requiring surgery, but that are not believed to be life threatening, Houston Police Department spokesman John Cannon said.

The gunman, whose name was not released, has a Houston address and was carrying a .40-caliber rifle. Police are investigating whether the man has a history of mental health issues.

Cannon said that every Occupy Houston participant interviewed said the man was not part of the movement and that they had never seen him before Monday night. Authorities are not aware of any other suspects or collaborators in the incident.

According to several witnesses, the man was wearing a black suit and white shirt when he entered Tranquillity Park from Bagby Street, shooting a rifle in the air about 5:15 p.m.

"I thought it was a joke," said Occupy protester Tim Jones. "It smelled like a cap gun."

Jones and others said they realized the weapon was real when the man reached the pedestrian bridge over the reflecting pool and fired into the water, sending ripples across the surface.

At one point, the man put the rifle to his own head, Cannon confirmed.

Within seconds, HPD special operation bike patrol officers H. Lam and A. Cantos were on the scene giving the gunman commands to drop his weapons. A standoff ensued on the bridge.

Occupy Houston peacekeeper who identified himself as Capital Baker said the man shouted "Kill me, kill me."

When the gunman failed to comply with numerous commands to drop the weapon and waved the gun toward officers, they feared for their lives and fired, Cannon said, hitting the gunman several times.

The incident, which saw bullets flying in a small, populated area during the after-work rush was over in a matter of minutes.

Witnesses said though the gunman pointed his rifle at people gathered in the park, he did not appear to be targeting the Occupy movement because he walked right by the main encampment on his way to the bridge. Bullet casings and an ammunition clip left on the bridge remained surrounded by crime scene tape for hours.

Amy Tepper, 18, said the gunman pointed his weapon directly at her. She was among about a dozen people involved in Occupy Houston who were whisked away in police cruisers to HPD headquarters for questioning.

"It startled me," she said.

City Councilman James Rodriguez reported seeing three flashes from his office window at the City Hall Annex, across the street from the park. It's unclear whether those were shots fired by the gunman or law enforcement.

cindy.george@chron.com

chris.moran@chron.com