In a social media message, the ferry company said: “Regretfully, P&O Ferries services are unable to run for the next few hours.
“Our Port Teams will guide you and travel will be arranged via an alternative operator.
“We apologise for the inconvenience this will have on your journey plans.”
It is understood that all ships in the P&O fleet - involving busy routes to Europe such as Dover - Calais - have been asked to “come alongside” in preparation of a company announcement.
No services will be running until the announcement and passengers due to travel today left confused over what is happening.
Councillor Matthew Armstrong, Deputy Mayor of Mid and East Antrim Borough Council, said the surprise announcement was “very worrying”.
Speaking on The Nolan Show, Cllr Armstrong said that although no further information was available at this time, it was very concerning for everyone at the Larne Port.
East Antrim MLA Stewart Dickson said he had received calls, including from a haulier, asking for information on what was going on.
“Very disturbing but particularly concerning for the Port of Larne,” said Mr Dickson.
Fellow East Antrim MLA John Stewart agreed it was very worrying for anyone planning to travel and also for all connected with Larne Port.
“This news will be deeply worrying.
“I really don’t understand the thinking behind this. We are trying to get our head around it.”
Travel journalist Simon Calder told the Nolan Show that the announcement had left passengers, including lorry drivers, “very bemused” about the situation.
“It appears to be a very unusual turn of events,” he said.