SAN FRANCISCO (KGO) — A magnitude 7.0 earthquake struck Northern California in Humboldt County, according to the USGS.

The NWS has issued a tsunami warning.

A magnitude 6.6 quake was initially reported, but was then upgraded by the USGS.

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There were no immediate reports of damage.

The earthquake was felt as far south as San Francisco, where residents felt a rolling motion for several seconds. Small aftershocks followed.

The Bay Area’s BART transportation system is experiencing significant delays due to the quake. There is no train service through the underwater Transbay Tube.

At least 5.3 million people in California were under tsunami warning following the earthquake, the US Geological Survey said in an amber warning that predicted localized but minimal damage.

The USGS estimates that more than 1.3 million people lived close enough to the quake that they could have felt it.

Phones in the Santa Cruz area buzzed with a tsunami warning from the National Weather Service that said: “A series of strong waves and strong currents could impact shores near you. You are in danger. Stay away from coastal waters. Get to high ground” or stay inland away from the coast now until local authorities say it is safe to return.

This is breaking news. Check back for updates.

The Associated Press contributed to this report.