About 20 demonstrators gathered in downtown Huntington Beach on Tuesday to protest President Trump’s proposal to open California’s coastline to new offshore oil and natural gas drilling for the first time in decades.

The protesters, who assembled along Main Street near Pacific Coast Highway, included members of activist groups Indivisible OC 48, Oceana and the Surfrider Foundation. They waved signs with phrases like “Drilling is killing.”

Another sign showed a picture of an offshore drilling rig and the message “This is so last century.”

Last week, Trump proposed opening much of the U.S. coastline to leases for offshore oil and natural gas exploration, a notion that in California’s case has been off limits since the Reagan administration in 1984.

“We’re here to say we’re not going to allow that to happen along the California coastline,” said Aaron McCall, chairman of Indivisible OC 48. Behind him, the group chanted “Surf’s up, rig’s down.”

“If there is an oil spill off our coast, that ruins our tourism industry,” McCall said. “That ruins our home. We shouldn’t allow that to be done.”

The president’s proposal, which is under public review and debate, has faced considerable backlash from West Coast governors, including California’s Jerry Brown, who contend it would pose environmental harm and ignore a need to transition away from fossil fuels.

Trump administration and industry officials, however, say the opportunity would significantly expand the nation’s energy production amid rising global demand.

“This is a start on looking at American energy dominance and looking at our offshore assets and beginning a dialogue of when, how, where and how fast those offshore assets could be or should be developed,” Interior Secretary Ryan Zinke told reporters last week. “Nobody is better at producing clean, quality, responsible energy than the U.S.”

bradley.zint@latimes.com

Twitter: @BradleyZint