Zim was granted the option due to an agreement to charter 10 vessels of the same class from July 6.

The LNG containerships are to be delivered during the fourth quarter of 2024, with Seaspan entering into agreements with a major shipyard to construct the ships.

The 12-year minimum charters total $900 million of gross contracted cash flow.

Since December 2020, Seaspan has announced 60 newbuild vessel orders and the acquisition of four second-hand vessels, all four of which have since been delivered.

"We continue to create value for our customers through differentiated services, operational excellence, and the ability to implement solutions tailored to our customers' changing requirements. The exercise of this option, with valuable vessel deliveries at competitive pricing, highlights the continued quality growth for both companies," said Seaspan CEO Bing Chen.

"The advanced design of these vessels demonstrates Seaspan and Zim's leadership in ESG initiatives and a more sustainable industry. With strong customer interest in this vessel size, we consider this category to be the natural successor to the aging global fleet of conventional vessels between 4,000 and 9,000 TEU," said Mr Chen.