There are delays of 20 minutes on services between between Par and Penzance, and between Truro and Falmouth Docks due to vandalism at Truro. Cancellations can be expected, with disruption expected to be ongoing until around 2pm.
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More than 150 boats are taking part in the World Pilot Gig Championships - the biggest in its 27 year history.
A minute's applause will take place during the Army-Navy rugby match in memory of Captain David Seath, who died during the marathon.
RNLI lifeguards will start patrolling beaches in the region this weekend as the 2016 summer season get underway.