Many of the 100 who got through suffered injuries and had to be treated in hospital.
It was the latest in a string of assaults in recent days at the crossings from Morocco to Melilla and Spain’s other enclave Ceuta, the rich European Union’s only land border with Africa.
Five migrants died last week in a similar attempt to use force of numbers to reach Ceuta; news reports said all were shot but it is still not clear by whom.
A police officer was also slightly injured in the assault on the fence which is between three and six metres high, though police gave no details.
About 60 young African men, hands and clothes shredded by the razor wire, waited outside Melilla city police station, hoping to avoid being sent back to Morocco by registering with police.
Several young African men, dazed and with blood-stained clothes and some without shoes, were ushered limping into ambulances at the police station.
The city’s military hospital was treating 39 of the migrants for cuts and bruises, an official there said.
The pre-dawn action was the second attempt this week by a large group of migrants to cross into Melilla.
The relatively new tactic is causing growing concern in Spain which dispatched troops last week to reinforce security.
The government has hired a company to build a new fence around
Ceuta and Melilla as rapidly as possible, Spain’s El Pais newspaper reported.
It will be a “metal labyrinth” two metres wide and 2.5 metres high, the report said.
Many wait their chance
The EU said yesterday it was ready to send experts to Morocco to help solve the immigration crisis.
Hundreds of migrants, many of whom have spent months and even years travelling across Africa, have been living in the woods on the Moroccan side of the 10km border, waiting to jump the fence.
The migrants, mostly from West Africa, build ladders from the trees which they use to scale the double fences guarded by Spanish police and troops and Moroccan authorities.
Spain does not have repatriation agreements with most African countries so cannot send the migrants back. Once over the fence, many get transferred to mainland Spain.
On Monday, about 650 sub-Saharan migrants charged border fences around Melilla, with 350 getting over when the fence collapsed.
About 135 people were injured in the rush, including seven police officers or soldiers.
Spain has ruled Melilla and Ceuta since the late 15th century but Morocco claims both regions as its territory.