P&O Ferries has paused its services "in preparation for a company announcement" later on Thursday.
The ferry operator said it was not going into liquidation but all ferries had been instructed to stay in port.
As a result some sailings scheduled for today have been cancelled, with passengers told to use other companies that sail their routes.
P&O services scheduled today include 14 between Dover and Calais and three between Liverpool and Dublin.
A spokesperson said: "P&O Ferries is not going into liquidation. We have asked all ships to come alongside, in preparation for a company announcement. Until then, services from P&O will not be running and we are advising travellers of alternative arrangements."
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