Several thousand migrants made their way to the border at dawn and over 500 managed to enter the border control area after cutting a fence with shears, the Spanish government's local delegation said in a statement.
Of these 130 sub-Saharan African migrants, "all of them men and apparently adults", managed to enter Melilla, it added.
Melilla and Ceuta, Spain's other tiny North African enclave, have the European Union's only land borders with Africa, making them a magnet for migrants.
Morocco deployed a "large" amount of forces to try to repel the assault on the border, who "cooperated actively" with Spain's security forces, the delegation said earlier in a separate statement.
Images on Spanish media showed exhausted migrants laying on the sidewalk in Melilla, some with bloodied hands and torn clothes.
In March this year, Spain ended a year-long diplomatic crisis by backing Morocco's autonomy plan for Western Sahara, going back on its decades-long stance of neutrality.
A month later, some 10,000 migrants surged across the Moroccan border into Spain's Ceuta enclave as border guards looked the other way, in what was widely seen as a punitive gesture by Rabat.
Rabat calls for the Western Sahara to have an autonomous status under Moroccan sovereignty but the Polisario wants a UN-supervised referendum on self-determination as agreed in a 1991 ceasefire agreement.
In the days just before Morocco and Spain patched up their ties, there were several attempted mass crossings of migrants in Melilla, including one involving 2,500 people, the largest such attempt on record. Nearly 500 made it across
