US labour dispute caused backlog
Twenty-nine West Coast ports in California, Oregon and Washington in the US are affected by the congestion, which stemmed from a labour dispute between dockworkers and their employers.
In July last year, talks began between the International Longshore and Warehouse Union and the Pacific Maritime Association after the contracts of 20,000 dockworkers represented by the union had expired.
Tension between the parties slowed freight traffic as the association accused unionised dockworkers of deliberately delaying cargo movement.
After months of negotiations, both sides finally reached a resolution last Friday with a tentative contract agreement.
But the cargo backlog at the Port of Los Angeles, the nation's busiest, is so bad that it could take up to two months to return to normal, Mr Gene Seroka, the port's executive director, told Bloomberg.