The world’s busiest container port, Yangshan in China’s business hub of Shanghai, is battling severe congestion wrought by dense fog, higher-than-usual volumes and the aftermath of a shake-up in shipping alliances, ocean carriers and port officials say. More than 100 container vessels are now waiting outside the port.

The fog started in early April and the congestion has recently worsened, with few clues to when it might ease. Average delays for ships arriving at the port jumped more than 42 percent to 53 hours between April 16 and 18 from the start of the month.

“We are making efforts to adjust and coordinate the entire port’s resources and making every effort to provide customers with the fastest service,” said a spokeswoman for Shanghai International Port Group.