Media playback is unsupported on your device Media caption The BBC's Tom Burridge said it is a "chaotic scene" in the disputed waters

Spanish fishermen have sailed into disputed waters off Gibraltar to protest about a reef put there by the British territory's government.

The fishermen say the reef restricts their right to fish, but Gibraltar says they should not be fishing there.

Gibraltar police said the protest, which lasted an hour and passed off without incident, ended at 10:20 BST.

The row over the artificial reef has led to tensions between the UK, Gibraltar and Spain in recent weeks.

'Not theirs'

Spanish fishing boats set off at about 09:00 BST to protest near the spot where 70 concrete blocks were dropped into the sea to create the artificial reef.

It had been suggested that they might try to remove the blocks, but the fishermen said before the protest that they would not attempt this.

The BBC's Tom Burridge, on board a Spanish fishing boat, described the situation as "chaotic and tense" as Spanish fishermen, and the Gibraltarian and Spanish police, weaved among each other.

Chief Inspector Castle Yates, of the Royal Gibraltar Police, said "about 38 Spanish fishing boats and seven or eight pleasure craft" were involved.

He said they crossed into Gibraltarian waters where police and the Royal Navy set up a cordon and "corralled" them.

"They tried to breach the cordon several times but they were not successful," he added.

Image caption Spanish fishermen gathered at the area where the reef was built using concrete blocks Image caption There was a heavy police presence as the protest got under way Image caption About 30 Spanish boats took part in the demonstration Image caption Reuters news agency said this image showed a Spanish Civil Guard boat colliding with a Gibraltar police boat while the protest took place Image caption In recent years the dispute over Gibraltar's sovereignty has taken the form of a clash over fishing rights previous slide next slide

At the close of the demonstration, Gibraltar's chief minister Fabian Picardo tweeted: "Big thank you also to Royal Navy, Gib Defence Police, HM Customs and Port Authority for their deployment too. Cool, professional and calm!"

Meanwhile, GBC News, Gibraltar's public service broadcaster, posted: "Spanish fishermen's demo in #Gibraltar waters seems to have passed without incident. Most fishing boats returning to La Atunara now."

The Spanish government has accused Gibraltar of creating the reef, which is located off the western runway of Gibraltar Airport, "without the necessary authorisation" in "waters that are not theirs".

It has said that, in building the reef, Gibraltar is contravening environmental laws and damaging Spain's fishing industry, because Spanish fishing nets are in danger of catching on the concrete reef blocks.

But Britain has said it was trying to encourage sea-life to flourish.

In response, Spain has imposed tougher checks at the border in recent weeks, leading to lengthy delays. It said the checks were necessary to tackle tobacco smuggling.

'Serious concerns'

But the UK accused Spain of breaking EU free movement rules.

Chief minister Mr Picardo has said he is not willing to make any concessions to persuade Spain to relax the controls.

On Friday UK Prime Minister David Cameron called EU Commission President Jose Manuel Barroso to raise "serious concerns" that Spain's extra border checks were politically motivated and "disproportionate".

The UK wants to resolve the row through "political dialogue", a Downing Street spokesman said.

Royal Navy warship HMS Westminster, which left Portsmouth last weekend, is due to arrive in Gibraltar on Monday in a visit described by the Ministry of Defence as "long-planned" as part of "a range of regular and routine deployments".

Spain disputes UK sovereignty over Gibraltar, a limestone outcrop near the southern tip of the Iberian peninsula, which has been ruled by Britain since 1713.

In recent years the dispute has taken the form of a clash over fishing rights. Both Spain and Gibraltar have claimed jurisdiction over the waters off the Rock, and both sides have complained about incursions into what they claim are their waters.