FREMONT, Calif. (KGO) -- Fremont Police are investigating what caused an explosion inside an apartment.
Authorities say around 9:30 a.m. crews responded to a report of an explosion at a complex off 37000 Waverly Terrace on Tuesday morning.
ABC7 News spoke with a resident who didn't want to speak on camera but said he felt the explosion right below him.
He said the entire building shook and thought initially it was a gas line.
Police and fire crews evacuated residents at adjoining units.
The initial investigation revealed a possible drug lab within the unit.
Drug detectives from the Major Crimes Task Force remained at the scene for hours.
Meanwhile, a man checked himself into Kaiser San Leandro around 1 p.m.
The hospital says when the patient got there several nurses started feeling ill.
Alameda County Fire Department hazmat responded, and the hospital closed their Emergency Department.
The fire department said a dozen staff members reported feeling nauseous.
The substance is still under investigation.
Kaiser said they got the all-clear to reopen their emergency department by 5:30 p.m.
Back at the apartment complex, many residents were surprised by the scene when they got home from work.
Some of the adjoining residents said they didn't have power.
The resident ABC7 News spoke with who lives on the third floor said he was told by management he was not able to return home for the night, so he was given a hotel voucher.
If you're on the ABC7 News app, click here to watch live