"Chinese citizens in the region (should) strengthen personal security measures, stay away from gatherings, crowded areas, or places with poor public security, and avoid going out at night or travelling alone," the consulate said in a statement.

They should also "closely monitor official announcements" and "raise their safety awareness", it added.

Security forces faced off with protesters in the city on Sunday, as unruly protests over federal immigration raids continued for a third day, with President Donald Trump deploying National Guard troops.

Trump, who has made clamping down on illegal migration a key plank of his second term, vowed the troops would ensure "very strong law and order".

The deployment in California -- the first over the head of a state governor since the Civil Rights era -- was "purposefully inflammatory," Governor Gavin Newsom said.

The National Guard -- a reserve military -- is frequently used in natural disasters, and occasionally in instances of civil unrest, but almost always with the consent of local authorities.