Los Angeles, California - Los Angeles was on Saturday placed under a state of emergency as fire crews fought a days-long battle against a stubborn warehouse blaze that filled the air with thick, black smoke.

"This is a major, multi-jurisdictional incident," Karen Bass, mayor of the second-largest US city, said in a statement, explaining that the state of emergency declaration will "ensure the city has the resources it needs."

The fire broke out Wednesday afternoon in a 500,000-square-foot frozen food warehouse, where burning foam insulation, suspected ammonia leakage and melting solar panels have complicated the firefight, officials said.

"The smell of smoke has reached most of the city, and we encourage everyone to limit exposure as much as possible," the Los Angeles Fire Department said in a Facebook post.

The fire has been contained to the warehouse but continues to burn, spewing fumes that smell of burning plastic and thick black smoke.

Residents in the area surrounding the warehouse – located in Boyle Heights – were initially warned to shelter in place, close windows and avoid breathing the air.

As the situation deteriorated, however, authorities opened 24-hour relief centers for people unable to otherwise escape the smoke.

Fire officials have since lifted those orders, reassuring people that the smoke is not toxic or different from a normal structure fire.

Air quality officials have, however, issued warnings for people in affected areas to avoid outdoor activity.

"This emergency declaration is crucial," said Council member Ysabel Jurado in a statement. "Residents have lived through days of smoke, shelter-in-place orders, disruptions to daily life, and ongoing questions about what this means for their health and well-being."

"I will continue pushing every level of government to bring the resources this community needs so that emergency response, air monitoring, hazardous debris removal, environmental remediation, and public health protections move forward with urgency."