Surfing has been put on hold at the Margaret River Pro because of flat conditions.

The fifth leg of the World Surf League tour was due to start on Sunday, with the competition window running until May 4.

Small surf at the main break on Sunday morning prompted event organisers to delay the round-one heats until at least Monday.

"It is looking like there will be a bit of promise happening in the forecast," competition boss Jessi Miley-Dyer said.

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"There's going to be a window even for tomorrow that we are going to look really closely."