Heavy ice is playing havoc with the ferry schedule between North Sydney and Newfoundland.

Each Marine Atlantic crossing is taking a couple of hours longer than usual, as the vessels make their way through the ice in the Cabot Strait.

Marine Atlantic has cancelled its daytime crossing today from North Sydney to Port aux Basques.

Darrell Mercer, speaking for Marine Atlantic, says the conditions are making it very difficult to maintain a regular schedule.

"The effect that we're seeing on that is of course, if it's taking two to three hours longer for each crossing then it starts to back up our schedule a little bit by the time we offload and load and move again. So that's why we've got some schedule impacts and advising customers to check our website before they head to the terminals," he says.

Mercer says the ice conditions are the worst they've been in years.

The ferry that normally travels from the Magdalen Islands to Prince Edward Island has been forced to change its route completely, as well.

It's running instead from the Magdalens to North Sydney.