ALGECIRAS: Tens of thousands of people marched through this southern Spanish town Saturday, calling for a British nuclear-powered submarine awaiting repairs in Gibraltar to leave at once.

Demonstrators say they fear a radiation leak of the docked submarine HMS Tireless and say the Gibraltar port is unequipped to handle any such emergency.

The submarine docked in Gibraltar, a British colony on Spain's southern tip, nine months ago after a crack was found in its cooling system. Britain later acknowledged the problem was more serious, saying a design flaw might be responsible for the damage, and recalled 12 similar submarines for checks.

During the two-hour demonstration just across the bay of Gibraltar, protesters, including politicians, union leaders and environmentalists, rallied behind a banner held aloft by children that read, "For our future."

The crowd shouted "Tireless Out" and song the Beatles hit "The Yellow Submarine." A few demonstrators waved signs demanding British authorities tow the submarine to England for repairs.

Police said 20,000 people attended the rally, but organizers put the number at 70,000.

The repairs on the submarine are scheduled to start Monday. Spanish Prime Minister Jose Maria Aznar has said he hopes the submarine will be removed by April.

The presence of the stricken submarine in Gibraltar has provoked concern and anger among Spaniards living nearby and strained the already sour relations between London and Madrid over the British colony. Assurances from both countries have done little to convince many of the 250,000 people who live near Gibraltar that there is no danger of a radiation leak.

Earlier in the week, authorities detained 10 Greenpeace activists who eluded Spanish police and British troops and climbed onto the submarine's deck to unfurl protest banners.

The HMS Tireless is one of 12 SSN Hunter Killer nuclear submarines in use by the British Royal Navy.

Located at the western entrance to the Mediterranean, Gibraltar has bedeviled relations between Spain and Britain since the land was ceded to Britain under the Treaty of Utrecht in 1713. (AP)