A fire broke out on an Italian-flagged transport ship, "Grande Europa", 25 miles south of the city of Palma on the island of Mallorca on Wednesday.
According to Spanish emergency services, two helicopters and three boats have been dispatched to assist in a rescue operation.
It is not immediately clear what caused the fire.
Grande Europa, a 20-year-old freighter, left Italy's Sardinia and was bound for the port city of Valencia in Spain.