Migrants tried to cross from Morocco into the Spanish enclave. Record 8,000 people poured over the border this week, escalating tensions between Rabat and Madrid.
Some tried to swim across to beaches patrolled by police after the unprecedented wave of arrivals earlier this week.
Spain's Prime Minister Pedro Sanchez has vowed to "restore order" in Ceuta, and on Wednesday accused Morocco of "disrespect" after the influx.
Some 5,600 migrants had already been sent back, Madrid said, but that did not stop more from trying to make the risky crossing Wednesday.
"Ceuta is Europe, this border is a European border and what happens there is not a problem for Madrid, but a problem for all" Europeans."
The record numbers of migrant arrivals have sent diplomatic tensions soaring between Madrid and Rabat.