MADRID - About 400 migrants stormed across a towering, triple-layer border fence from Morocco into the tiny Spanish territory of Melilla on Wednesday, one of the biggest crossings in nearly a decade, an official said.

More than 1,000 sub-Saharans joined in the dawn assault on Melilla, a tempting target for Africans desperate to reach Europe because it forms one of the only land crossings along with another Spanish territory, Ceuta, to the west.

About 400 of them managed to breach the three layers of seven-metre (23-foot) high border fence, the president of the city of Melilla, Juan Jose Imbroda, told Spanish public radio RNE.

"It was a very large number," he said. "An exterior part of the barrier was pushed over." Imbroda said the Moroccan authorities cooperated well with the Spanish border guard. "

The Guardia Civil police deployed in large numbers but it was hard to stop it," he added.

Melilla, which lies on the northern coast of Morocco, is enclosed by an 11-kilometre (seven-mile) long border fence running in a semi-circle up to the Mediterranean.

Nevertheless, migrants gathering in large numbers on the Moroccan side have repeatedly managed to breach the defence.

On March 18, about 1,000 migrants rushed the fence in foggy weather and some 500 migrants managed to get across, the largest number since 2005, Spanish authorities say.

Depending on treaties with the immigrants' countries of origin, some are repatriated and others are allowed to stay in Spain.

Meanwhile they wait in government-run reception centres. The centre in Melilla is built to house 480 immigrants but it is now holding about 2,000, Imbroda said. "Imagine the huge problem we will have this morning with 400 more on top of the 2,000 people already there," he said.

The number of Africans trying to cross into the two Spanish territories has surged over recent months. Spain's government has demanded more help from the European Union to deal with them.

On February 6 about 15 migrants drowned in Moroccan waters while trying to swim to the other Spanish territory in Africa, Ceuta, from a nearby beach.

Rights groups and witnesses accused Spanish security forces of firing rubber bullets at the migrants in the water.

The government admitted using rubber bullets but denied its forces had targeted the migrants directly. It later banned civil guards policing the border from using rubber bullets to repel migrants.