Cyclone Sandra has formed in the Coral Sea off the Queensland coast.

The Bureau of Meteorology says the category one system formed overnight and is situated about 1,000 kilometres north-east of Mackay.

It is moving north-east at about 13 kilometres per hour.

The bureau says Sandra is expected to intensify over the next 24 hours before turning southwards.

"It's going to eventually start turning around to the east and the south-east and eventually south, so it's just going to keep turning around to the southern ocean off our coastline, or well off our coastline," senior forecaster Brian Rolston said.

It is predicted the system will remain well out to sea until at least the middle of next week.