Carbon monoxide was confirmed to be present in an apartment building in Koreatown where one person was found dead and at least three others had fallen ill on Thursday, officials said.
It was the second death in recent days at the apartment building, located at 920 S. Hobart Blvd., according to the Los Angeles Fire Department.
The four-story, 48-unit building was fully evacuated after officials responded around 5:45 p.m.
Authorities were first called to the scene after one resident complained of unusual, flu-like symptoms. A short time later, a person was found dead on the floor above, firefighters said.
The hazmat experts on scene were using "sophisticated handheld sensing equipment" to search and evaluate all the apartments in the building, LAFD said. One resident told KTLA crews were working to determine whether residents would be able to return home Thursday night.
Authorities were unsure of the specific cause of death in the previous fatality and did not say exactly when that person died. Medical officials also have not confirmed the cause of death of the person found Thursday, or provided a diagnosis on those who are ill.
One resident said he constantly heard an alarm going off, as if its battery was dead, while another said her carbon monoxide alarm had gone off multiple times in recent weeks.
Authorities were continuing to survey the structure, built around 1928.
No further details were immediately available.