By Jim Forsyth

SAN ANTONIO (Reuters) - Two people were killed and five others hospitalized after gunmen in a car opened fire on a gathering of more than 100 people in a parking lot in San Antonio, police said on Tuesday.

Interim San Antonio Police Chief Anthony Trevino said some people in the crowd may have returned fire, calling the Monday night incident a "gunfight."

He added the incident looks to be gang related and many in the crowd had gathered in the parking lot for an event to mark the Martin Luther King Jr. Day national holiday.

As many as 20 shell casings were found in the parking lot, police said. No arrests have yet been made.

Police said the situation was chaotic when they arrived, with individuals holding guns and others throwing rocks and bottles. About 50 officers were dispatched to restore order.

One man was dead on the scene and another died en route to a hospital. Two men and three women were also hospitalized for gunshot wounds and other injuries. The names of those killed have not been released.

(Reporting by Jim Forsyth; Editing by Jon Herskovitz and James Dalgleish)