Firefighters late Tuesday were investigating reports of a strong odor in Vallejo and were asking residents to shelter in place.
The Vallejo Fire Department said it received more than 500 calls reporting a strong odor in the Glen Cove and Beverly Hills Park neighborhoods in South Vallejo. Firefighters reportedly were able to rule out natural gas and refinery emissions as the source of the odor.
Vallejo fire officials said local hospitals were reporting multiple patients arriving as a result of the mysterious odor. Patients complaining of burning in their throats and noses were arriving at Sutter Solano Medical Center in Vallejo, Kaiser Vallejo Medical Center and Northbay Medical Center in Fairfield.
Fire officials later determined that the odor was coming from outside Vallejo. The shelter-in-place warning remained in effect into Wednesday morning.
Late Tuesday night, Coast Guard Lt. Steven Dross said a sheen had been confirmed on the water in a number of mostly connected locations in and around Vallejo as well as San Pablo Bay and the Carquinez Straits.
Coast Guard personnel at Station Vallejo could see the sheen on the water from the docks, according to Dross, but the nature of the substance has not yet been determined, and it is not yet clear whether the sheen is connected to reports of an unusual odor nearby.
Pollution responders were investigating, Dross said.
Residents were advised by the city's Emergency Operation Center that there is an unknown odor in the air, primarily in the south portion of Vallejo. PG&E and public safety officials were working to determine the cause.
NBC Bay Area's Terry McSweeney and Bay City News contributed to this report.