A flotilla of giant container ships is anchored in San Francisco Bay waiting to unload cargo at the Port of Oakland, the result of a disruption that has clogged the West Coast’s major commercial arteries.

The traffic jam in the bay, from ships bringing in imported goods, is only part of the problem. Exports are also threatened, including perishables from the Central Valley that are stuck in limbo.

The increase in traffic has caused a pileup of containers on the docks, which have to be shipped out to make room for more, and that has led to a backup of goods arriving at the port for shipment overseas. “The system is backed up all way to the Midwest,” said port spokesman Roberto Bernardo.

Some ships have even been forced to wait outside the Golden Gate until anchorages become available.

By Friday evening, 16 vessels requiring a deep berth were lined up waiting to dock at the Port of Oakland.

“It’s definitely busy,” said Lt. Commander Nicolette Vaughan, chief of inspections for the Coast Guard’s San Francisco sector.

An average of 12 to 15 ships a week have come to Oakland in recent months, surpassing anything seen in the past decade, said Bernardo.

Epic congestion at Southern California ports “has caused a lot of these cargo ships to come up here to Oakland,” he said.

The ports of Long Beach and Los Angeles are jammed with ships waiting to unload, in part due to a lack of trailers to haul goods from the port, a work slowdown by dock workers and an increase in huge container ships.

The huge ships are also a problem in the San Francisco Bay, which is only deep enough to handle them in certain areas, said Bernardo.

“There are some areas in San Francisco Bay that cannot accommodate these megaships,” he said.

The U.S. Coast Guard warned 10 days ago that shippers “should be prepared to make alternate mooring arrangements or expect that the vessel will need to remain at sea until safe anchorage space becomes available” in the bay. On Wednesday, the Coast Guard followed up with a warning that there were no anchorages available for big ships with drafts in excess of 25 feet.

The port’s import volume between September and November was up 4 percent from the same period a year ago, a significant increase representing thousands more shipping containers than normal. The flow is expected to ease in the new year as the holiday period passes, but other problems remain.

The snarl at the port that has been amplified by an equipment shortage, for example, and protracted labor negotiations since the International Longshore and Warehouse Union has been without a contract since July 1.

ILWU spokesman Craig Merrilees said the logjam is nothing new and isn’t the union’s fault. “The congestion problem has been happening up and down the coast for most of the year,” he said, “and long precedes any allegation made by employers of a slowdown.”

Merrilees said one problem is the growth of mammoth ships capable of carrying as many 14,000 containers. “Not too long ago, a ship carrying five or six thousand containers was considered a monster,” he said.

But the Pacific Maritime Association, which negotiates labor contracts for shippers and terminals, has blamed the traffic jam on worker slowdowns at some ports and “intermittent walkoffs” at the Port of Oakland.

On Monday, the association requested federal mediation.

Contact Pete Carey at 408-920-5419 Follow him on Twitter.com/petecarey