The Port of Oakland, one of the busiest West Coast ports and a hub for trade with China, is seeing exports fall as the trade war escalates.

In July, exports fell 7.3 percent year over year — their fifth monthly drop in a row.

“There’s been some decline over the last few months,” said Michael Zampa, a spokesman for the port, which supports more than 73,000 jobs in the Bay Area and is the third-busiest U.S. port on the West Coast by container volume.

“It’s still too early to tell” if the primary reason for the drop is tariffs, he said. China’s restrictions on recycled paper, which is used to package retail goods, has also been dampening exports, Zampa said.

Last week, the Trump administration added tariffs on $16 billion in Chinese imports that will go into effect next Thursday. The products affected mostly include manufacturing materials like oils and plastics. The tariffs are on top of $34 billion in Chinese goods already subject to U.S. tariffs since July, which sparked equivalent Chinese tariffs on American goods.

The Port of Oakland’s imports jumped in June by 8.7 percent year over year to a record-high volume, which the port attributed in part to Asian companies trying to beat the tariffs. Imports were down slightly in July by less than 1 percent year over year. Some ships arriving from Asia fully loaded have gone back empty.

Smaller Bay Area ports are also experiencing or anticipating pain from trade tensions.

Richard Aschieris, director of the Port of Stockton, said that last year four or five ships carrying steel would typically arrive each month. But only one ship is scheduled to dock in August, putting 50 to 70 people out of work, he said. In March, the U.S. imposed a 25 percent tariff on steel imports worldwide, though it later exempted some countries.

“We live in an economically disadvantaged area, and we are trying every which way we can to create jobs and economic improvement for people that live in the Central Valley,” Aschieris said. “We have fewer people working because we don’t have those ships coming in.”

Aschieris said that, earlier this year, Union Pacific, a railroad company, was trying to bring in steel from Japan. The tariff raised the cost of a shipment by $5 million, so it sat in San Francisco Bay for nearly a month until the partners came to an agreement on who would pay what portion of the extra sum.

Jim Matzorkis, executive director of the Port of Richmond, said exports haven’t declined, but companies are worried.

“There’s concern over what the impacts will be,” he said. “I think it takes a couple of months to really get a feel for” the impacts.

Meghan Horrigan, spokeswoman for the Port of Redwood City, said it was “too premature” to report any impacts of the tariffs on its business.

The Port of Los Angeles, the nation’s largest port, has gotten a boost from the tariffs — at least so far. On Wednesday, the port reported record-high shipping activity in July, as Chinese exporters rushed shipments in ahead of the enactment of sanctions.

The Port of Oakland, for its part, expects a clearer picture of the effects of tariffs this month, as the peak shipping season begins.

“August will be a bellwether,” Zampa said.

Roland Li and Wendy Lee are San Francisco Chronicle staff writers. Email: roland.li@sfchronicle.com wlee@sfchronicle.com Twitter: @rolandlisf @thewendylee