This story originally published on JOC.com.

More than 100 container ships are delayed outside the Shanghai port of Yangshan as a combination of dense fog and larger vessels assigned to the busy terminal causes worsening congestion.

Fog is common at this time of the year in North China, and it began affecting operations beginning in early April at Yangshan, situated about 15 miles off the coast of Shanghai, according to CargoSmart.

But even as the fog rolls in, larger vessels that have also come calling at the terminals under the new alliances, and the reaction by shippers to the new vessel groupings, appears to be exacerbating the weather-related delays. Forwarders are reporting a growing imbalance in container volumes as shippers made bookings earlier to secure the space ahead of the April 1 alliance launches.

Even though there were usually "quite a lot [of] vessels" waiting outside Shanghai Port, in the past few days CargoSmart had found that the numbers were rising sharply to more than 100 recorded today.

In conjunction with the worsening congestion, compared with the first two weeks of April, the average vessel berth time and average vessel size have increased by around 6 percent. "It seems that the impact to berth time is not significant. However, the vessel waiting time may be prolonged," the CargoSmart spokesperson said.

Maersk Line has been affected by the delays from what it called "seasonal bad weather" and the Shanghai International Port Group had shifted some port calls from Yangshan to its other terminals in the city.

A container line executive at a large Asian carrier told JOC.com that congestion at Yangshan appeared to indicate that the port was struggling with the increased volumes and bigger vessels that have been assigned to the terminal.

"This affects primarily Asia-Europe and trans-Pacific sailings, with knock-on effects in all other ports as the big vessels have less flexibility to switch berths and terminals in the subsequent ports," he said.

The supply chain head of a major European shipper said the congestion had also spread to the port of Qingdao, north of Shanghai. "But so far it all still works and we are lucky," he said.

The Ocean Alliance, THE Alliance, and the 2M-plus Hyundai Merchant Marine launched on April 1, completely redrawing the existing vessel sharing agreement (VSA) structures. These VSAs were in addition to various independent carriers including newcomer SM Line, which also began its new trans-Pacific service last week.

Compared against the peak season deployment of summer 2016, total vessel capacity planned for this summer will be 2 percent higher, according to Alphaliner. At the same time, the number of deployed ships is set to fall as carriers continue upgrading services to larger vessel sizes.

An analysis of the vessel deployment by size shows significant increases in ships ranging from 14,000 to 20,000 teus, as well as the 5,500- to 10,000-TEU size segment.