The collapse of a convention centre being built northwest of the Saudi capital left more than 50 workers trapped under rubble on Monday, official media said.

The collapse of a convention centre being built northwest of the Saudi capital left more than 50 workers trapped under rubble on Monday, official media said.

The collapse "happened at noon and resulted in more than 50 workers being trapped", the Saudi Press Agency said, adding that four wounded were recovered from the building site for Qassim University.

Bandar al-Roshodi, the university spokesman, told Saudi television news channel Al-Ekhbariya that the workers were mostly from Pakistan.

"Until now we are searching," he later told AFP.

The trapped workers were of "different nationalities," Roshodi said. Asked about the chances of more survivors, he said: "We have hope, God willing."

Pictures from the scene showed a sprawling but low-level construction site, where many steel support rods had collapsed along with other parts of the structure.