The city of Huntington Beach on Saturday night closed ocean waters from the Santa Ana River jetty to the city pier due to an oil slick that the Coast Guard was investigating earlier in the day, officials said. The city of Newport Beach also said the slick — what it called a “large oil spill” — was expected to come ashore late Saturday between the Balboa Pier and the Corona del Mar Main Beach.

The Coast Guard said around 12:15 p.m. Saturday it was responding to an oil slick about 11 miles long off the coast of Huntington Beach.

It wasn’t immediately known what caused the possible leak.

The Newport Beach Fire Department planned to send a rescue boat out toward the site to get more information on the approximate location, after the crew finished assisting with the Pacific Airshow in Huntington Beach for the day, Battalion Chief Brent Jacobsen said.

The department said it had heard secondhand and over boat radio that people had seen an oil spill between three and seven miles off the coast, Jacobsen said. The spill was initially reported off the coast of Newport Beach.

“We don’t have a complete picture yet,” he said.

Hazardous materials teams were on site to deal with any impacts.

This is a developing story. Please check back for updates.