Spain has unveiled a multi-million-dollar surveillance system to protect its southern coast from the immigrants who brave treacherous waters to enter the country.

Radar sensors and night-vision cameras will monitor the 110 kilometres (70 miles) of Spanish coastline closest to Morocco, where many clandestine migrants start their journey.

The Integrated External Vigilance System, which has cost $140 million to construct, has been billed as the first of its kind in Europe.

It comes amid growing concerns within the wealthy European Union over illegal immigration, which many political leaders fear fuels the electoral chances of far-right movements against mainstream parties.

Perilous journey

The most popular route into Spain - for thousands of illegal immigrants is across the Strait of Gibraltar, which is just 14 kilometres wide at Tarifa - Europe's southernmost point.

The trip, often undertaken in packed rubber boats, is a hazardous one.

The Spanish police say they have rescued 730 people from the sea in the Strait since 2000, while humanitarian organisations say several thousand are likely to have drowned in that period.

Earlier this month, the bodies of 13 illegal immigrants were washed up on the shore near Tarifa.

Many who do make it alive are expelled shortly after arrival. Last year Spain sent nearly 45,000 immigrants back where they came from.

The issue has become a major bone of contention between Spain and Morocco, amid already strained relations.

It is thought the new surveillance system is likely to further exacerbate those tensions.

As well as intercepting illegal immigrants, Spain also hopes to combat drugs trafficking across the Strait - which primarily involves hashish from Morocco.

After the system becomes fully operational, Spanish authorities intend to extend the network to cover the entire southern coast as far as the French border.