The 2020 Rotary Across Wales Walk has been cancelled due to the "escalation and uncertainty" of the coronavirus outbreak.
The Rotary Clubs of Newtown, Llanidloes and Machynlleth said it made the announcement with a "very heavy heart" on Wednesday morning.
The event - a feature of the Mid Wales calendar since the mid 1970s - was due to take place on Saturday, June 20.
In a statement, organisers said: "The decision has not been taken lightly, but with such escalation and uncertainly of what lies ahead our over-riding responsibility toward the safety of our participants and event team is our priority.
"Enormous apologies and we hope to welcome you next year, to the new route and first finish in the beautiful town of Montgomery."
Details about refunds or deferrals will be revealed shortly. The next event is planned to take place in 2021 on Saturday, June 19.
Anyone who has questions can contact the organisers on the Rotary Across Wales Walk Facebook page.
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