"Five hundred immigrants attempted to forcibly enter (Melilla)... Sixty-five managed to penetrate," Melilla police headquarters said in a statement on Wednesday.
In Morocco, which surrounds tiny Melilla, a source at the Interior Ministry confirmed the latest assault, but said "only a very few" people had broken through.
Melilla police chief Jose Fernandez Chacon welcomed the day's "close collaboration" with the Moroccan authorities.
Recent months have seen a sharp increase of such incidents in Melilla and its twin, Ceuta, involving people from many African countries determined to escape poverty and start a new life in Europe.
The latest assault took place in the Pinares de Rostrogordo zone where the perimetre fence has yet to be raised from three to six metres high, as is the case around the rest of the enclave, according to private Spanish radio Cadena Ser.
Medics in the zone treated many immigrants for cuts and bruises, and two were still under observation, police said, adding that two members of the Civil Guard had also been injured.
The Africans scaled a part of the
perimetre fence yet to be raised
About 15 immigrants had to have plaster casts applied.
Two new Civil Guard anti-riot units were joining six other units on site, the police statement said.
A helicopter with night vision cameras joined the Civil Guard's surveillance efforts on Tuesday night. Spain's army also began to patrol the zone last Thursday.
A tired and nervous Malian who managed to cross into Melilla on Wednesday told AFP that the would-be immigrants battled Moroccan police with stones, and were then attacked with tear gas and truncheons by Spain's Civil Guard before they dispersed onto Spanish soil.
Another Malian, Ali Traoure, said that the Spanish Civil Guard had used rubber bullets.
The new invasion took place before dawn the day after local government official Jose Fernandz Charcon announced that a third metal barrier would be set up to reinforce the border with Morocco.
Deputy Prime Minister Maria Teresa Fernandez de la Vega, who is also the spokeswoman of Spain's Socialist government, was due on Wednesday afternoon to meet the Conservative local government chiefs of Melilla and Ceuta, who have strongly criticised the administration's management of the crisis.
Many are determined to escape
poverty in their countries
EU justice and security commissioner Franco Frattini on Tuesday said the bloc would shortly be sending a technical mission to investigate the worsening situation on the southern coast of the Mediterranean.
Seven African would-be immigrants have died since the beginning of the summer during similar assaults, including five in Ceuta on Thursday.
On Monday 135 people were injured when about 650 stormed Melilla.
About 300 people broke into the same enclave in two mass stormings of the barrier, involving nearly 1000 people, in a similar incident.
Spain has recently been accelerating plans to raise the border fence, equipped with infrared cameras and movement detectors, while Morocco is increasing police operations in forests bordering the enclaves.
After Wednesday's incident, Moroccan police arrested 85 immigrants, including 13 women, bringing the total number of such arrests since the beginning of the year to 6167.