"This is an operation that is part of the fight against illegal immigration," said an official speaking on behalf of local authorities in Tangier.
The official estimated that between 1,600 and 1,800 people had been "moved to cities where living conditions are better".
But a representative of a Moroccan human rights organisation told AFP authorities detained and forcefully relocated the migrants, calling the move "illegal".
"The authorities continued Saturday to drive migrants by bus from Nador and Tangier to the town of Tiznit, near Agadir" in the country's south, Omar Naji of the Moroccan Human Rights Association said.
"The operations began on Tuesday and the authorities arrested hundreds of migrants in camps near Nador or in homes in the city," he said.
He was unable to specify how many migrants had been expelled from Tangier.
"There arrests are illegal because they are without judicial warrants" and Morocco, Spain and the European Union are "responsible", said Naji.