One person is dead after a shooting close to a California polling station.

One person is dead after a shooting near a US polling station in California, with the "heavily armed" shooter later found dead following a standoff at a home in Azusa.

The Los Angeles Times has reported officials said they didn't know whether the man — who was described as heavily armed — was killed by police or from a self-inflected gunshot wound.

At two people were critically injured after the polling station in Azusa, east of Los Angeles, was placed into lockdown.

Officer Jerry Willison of the Azusa Police Department told the Los Angeles Times, "this is a very volatile and critical situation".

A witness and nearby resident told the LA Times that he was outside his home with his wife when saw a heavily armed man fire at least 10 rounds into a group of people.

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The witness also told the LA Times that the shooter, dressed in a white shirt and black trousers, then ran inside a nearby house.

Azusa Police Chief Steve Hunt said it was too early to determine whether the violence was in any way related to today's US election.

One voter told CNN he was inside the polling station when shots were heard, after which people ran in from outside before officials locked the doors.

A female voter told CNN said that officials were not allowing people to leave the building and that updates were not being provided so as not to scare children.

It is unclear at this stage exactly how close the shooting was to the polling station, or if it was related.

Azusa is roughly 45 kilometres east of Los Angeles.

- Stuff and Reuters