A major highway in South Australia is closed as emergency services respond to reports of a serious crash involving two trucks.

SA Police said crews were called to the Eyre Highway about 27 kilometres west of Yalata at 6:45am after reports two trucks had crashed.

Police expect the highway to be closed all day and said all motorists should park at Yalata, about 200 kilometres west of Ceduna, or other major service stations.

Posted , updated