MADRID (AP) — Spanish authorities say hundreds of migrants have stormed border fences separating Spain's North African enclave of Ceuta from Morocco.

Spanish news agency Europa Press quotes Ceuta police saying as many as 400 migrants may have made it onto Spanish soil in the assault, shortly after dawn Thursday.

Sub-Saharan Africans living illegally in Morocco try to get to Europe each year by climbing rows of 6-meter-high (20-foot-high) barbed-wire fences surrounding Ceuta and Melilla, Spain's other North African enclave.

Thursday's mass charge added to pressure on Spanish authorities from a recent wave of migration.

The International Organization for Migration says so far this year more than 22,700 migrants have arrived in Spain — three times more than in the same period last year. Almost 20,000 of them arrived by sea.