A murder-suicide has killed two people at the University of California, Los Angeles, shutting down the campus for two hours as officers in camouflage and tactical gear responded to reports of a shooting.

Charlie Beck, Los Angeles police chief, confirmed one man shot another and then himself on Wednesday in the engineering building and that police recovered a gun at the scene.

"There are no suspects outstanding and no continuing threat to UCLA's campus," Beck said.

Police recovered what may turn out to be a suicide note, he said.

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A law-enforcement official said the victim was a mechanical engineering professor.

William S Klug was shot in the engineering building office on Wednesday morning, according to the official, who has knowledge of the investigation but was not authorised to publicly discuss it.

Colleagues of Klug told the Associated Press news agency he was a married father of two and a kind, gentle person.

Groups of officers stormed into campus buildings that had been locked down on Wednesday [Reuters]

Charles Knobler, UCLA biology and chemistry professor, said those who knew Klug are in shock.

He described the professor as "a very lively, lovable, likeable guy".

The shooter has not yet been identified.

UCLA, with more than 43,000 students, is in the Westwood section of Los Angeles and one of the more well-regarded schools in the University of California system, known for its successful sports programme.

Classes were cancelled on Wednesday, but they are expected to resume on Thursday.

'Extraordinary grace'

Los Angeles Mayor Eric Garcetti praised the people of UCLA for "extraordinary grace and calm" and lamented the violence at a place of learning.

"I am heartbroken by the sight of SWAT teams running down avenues normally filled with students, and angered by the fear that one person with a firearm can inflict on a community," Garcetti said.

The response to the shooting was overwhelming: up to 200 police officers approached the scene, fearing the shooter might still be active and university officials ordered the campus to be locked down.

UCLA, with more than 43,000 students, is in the Westwood section of Los Angeles [Reuters]

The officers stormed into buildings that had been locked down and cleared hallways as police helicopters hovered overhead.

Advised by university text alerts to turn out the lights and lock the doors where they were, many students let friends and family know they were safe in social media posts.

Some described frantic evacuation scenes, while others wrote that their doors were not locking and posted photos of photocopiers and football tables they used as barricades.

Those locked inside classrooms described a nervous calm. 

Source: Agencies