California has declared a state of emergency as a massive storm begins to slam the state, causing flooding, downed trees and even glass to fall off skyscrapers in Downtown San Francisco in a weather event that could last through the end of the week.

“California is mobilizing to keep people safe from the impacts of the incoming storm," Gov. Gavin Newsom said. "This state of emergency will allow the state to respond quickly as the storm develops and support local officials in their ongoing response.”

An emergency declaration allows the state to mobilize its National Guard and call on the federal government for support with local highway response efforts. The state also announced it has opened an operations center to stay on top of the emergency.

The bulk of the storm is expected to hit the Bay Area on Wednesday afternoon, with San Francisco city officials predicting widespread flooding and power outages, saying the city's systems are likely to be overwhelmed.