Thousands of Spaniards, in a weekend demonstration, demanded the closure of an offshore gas storage site linked to hundreds of small earthquakes.

A crowd estimated at between 3,000 and 6,000 protesters took to the streets of the Mediterranean coastal city of Alcanar Sunday, calling for the shuttering of the Castor gas storage plant, operated by the Spanish company Escal UGS, the Spanish daily El Pais reported.

The undersea storage site, located 13 miles off the coast of Castellon province in Valencia, has been identified by Spanish Industry Minister Jose Manuel Soria as the likely cause of nearly 500 small tremors recorded in the area in recent weeks.

Castellon prosecutors last week opened an official investigation of the Castor project to determine if it is indeed responsible for the rising number of earthquakes, the most intense of which registered a 4.2 magnitude.

Some 22 small temblors were recorded Thursday, measuring between magnitudes 3.7 and 3.5, with small quakes continuing over the weekend.

Protest organizer the Platform in Defense of the Land of Senia said 6,000 people attended Sunday's demonstration, while the local police put the number at 3,000. The protesters included hundreds of families from all areas of northern Castellon who marched on the boardwalk of the village with signs bearing such slogans "No to Castor," the newspaper said.

Among the targets of their ire were Escal UGS President Reccared del Potro.

"He and his partners should be held responsible (in) the criminal proceedings the prosecution opened on Friday," the group's manifesto stated. "The anguish we suffer in this territory and the great danger we face call for a quick emergency response from the government.

"They should not wait any longer to declare, with all the force of law, that the business of a few should not endanger the welfare of all."

The group told El Pais they are gathering documentation to lodge complaints with the European Court of Justice and the Spanish courts aimed at permanently closing the Castor project, in which some 100 million cubic meters of gas have so far been injected into a depleted undersea oil reservoir capable of holding 1.3 billion cubic meters of gas.

The process was halted by the government Sept. 26, when it commissioned technical reports from the National Geographic and Geological and Mining institutes to establish the relationship between the earthquakes and the injection of gas in Castor the system.

In the meantime, local residents say they can't sleep at night for fear of more earthquakes, which have triggered memories of a deadly 2011 in Lorca, Spain, that killed nine people and injured 100.

Mario Sancho of Alcanar told the Spanish newspaper 20 Minutos he was especially frightened by Thursday's 4.2-magnitude quake.

"I went to lie down ... and I noticed that the bed was shaking," he said. "I panicked, I looked up and thought it was a burglar. After it stopped, I turned on the light, looked around the house and went outside. I sat down and at 1:30 a.m., and noticed a second quake, but shorter and not so intense."