Methane gas from the sea floor caused a foul odor on Sunday that prompted nearly 100 emergency calls from residents reporting the stench from Santa Monica to West Los Angeles, officials said.

The odor, which smelled like sulfur, was first reported late Saturday, air quality officials said. The smell wafted in from the Santa Monica Bay.

Justin Walker, a Santa Monica Fire Department spokesman, said hazardous-materials crews found small increments of methane gas in the air at 8:30 a.m. 

The amount of methane in the air was not considered dangerous, Walker said, adding he's heard of this type of incident happening up to six times in the last four years.

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Hazardous-materials crews were called out after dispatchers reported some 80 calls to 911 of residents reporting the stench.

Methane is usually released when the tectonic plates shift, Walker said. This shift was small and did not cause an earthquake, he said.

A cold weather front that moved in overnight and brought onshore winds with it caused the smell to waft inland, he said.

"The marine layer vacuumed it up because it had nowhere to go out," Walker said.

Inspectors from the South Coast Air Quality Management District, Southern California's air pollution control agency, were also investigating.

Maria Carlito Covarrubias, writing on the NBC4 Facebook page, said she smelled the odor Saturday night at about 11:45 p.m.

Another Facebook user, Summers McKay, said she called her building manager because she was worried that the smell was a gas leak.