The declaration, which is usually issued in times of natural disaster, frees up resources that can be used to help those affected in the county, home to a large number of undocumented migrants and one of the most diverse parts of the United States.
Supporters of the move say broad-based migrant raids being carried out by masked agents are untargeted and focused on people who speak Spanish or appear to be Hispanic.
They claim the fear the raids cause is preventing breadwinners from going to work and creating genuine hardship in immigrant communities, with one recent survey finding average weekly earnings among immigrants down by over 60%.
Janice Hahn, one of the county supervisors who voted 4-1 in favour of the declaration on Tuesday, said it was needed in response to “the fear, the pain and the disorder these… raids are causing our community.”
“We have entire families who are destitute because their fathers or mothers were taken from their workplaces.
“I want our immigrant communities to know that we are in this emergency with them, we see them and we understand what they are going through.”
Raids by armed Immigration and Customs Enforcement (ICE) agents, as well as other officials from agencies under the Department of Homeland Security, sparked uproar in Los Angeles when they unfolded several months ago.
Weeks of unruly protests were met by Trump’s decision to send National Guard soldiers onto the streets of America’s second largest city, a move criticised as heavy-handed and inflammatory by critics.
The raids have spread to other, mostly Democratic-run cities, including Chicago and Portland, Oregon, where the federal government has also tried to send National Guard troops.
Tuesday’s decision by county supervisors opens the door to a later eviction moratorium and other tenant protections for those who have fallen behind on their rent because of the raids.
Board of supervisors chair Kathryn Barger said she was voting against the proclamation because she feared it would simply prompt costly legal action from the federal government.
“We need real solutions, not symbolic gestures,” she said in a statement after the vote.
“I’ll continue to support targeted, community-centred programmes like legal aid and rental assistance that provide meaningful help to vulnerable families while respecting legal limits, protecting County resources, and preserving public trust.”