The Danish owner of the world's largest container shipper, Maersk Line, said its computer systems were among those hit by the global Petya cyber attack, causing problems processing orders and delaying cargo.
AP Moller-Maersk said the cyber extortion, which has disrupted businesses around the globe, has also led to congestion at some of the 76 ports run by its APM Terminals unit, including in the United States, India, Spain and the Netherlands.
"It will have an impact on vessels or cargo that loaded yesterday, today and maybe also tomorrow," Maersk Line chief commercial officer Vincent Clerc said on Wednesday.
Due to limited access to some of its computer systems, Maersk, which handles one out of seven containers shipped worldwide, also has problems processing orders taken just before the breakdown, Mr Clerc said.
When the attack began, on Tuesday afternoon in Europe, Maersk decided to take down a number of systems as a precaution. The company is working on a technical recovery plan, Mr Clerc said.
For now, Maersk is using alternative channels to take orders manually and to communicate with customers, he said.
He said no data had been lost due to the cyber attack, and that the company would be able to resume operations "right away" once the issues were solved.
Maersk said operations at some APM Terminals around the world, including Los Angeles, were affected.
Two APM terminals in Rotterdam, Europe's busiest port, are still out of commission. A spokesman said knock-on effects for the port as a whole were minimal, with a slight delay in operations.