According to Rajoy, only central government has the constitutional right to call a referendum and then it would almost certainly have to include the whole of Spain.
Mild winter weather and blue skies helped long lines form at many polling stations early Sunday. By 1 p.m. (7 a.m. EST), the Catalan government calculated that voter turnout was higher than in the previous seven elections dating back to 1988.
Rajoy has said that talk of independence is a side issue to the country's real problem, which is to find a way to create employment and address its deficit.
While Rajoy is immersed in combating Spain's worst financial crisis in decades, Mas claims Catalonia is being asked to shoulder too much of the tax burden and that it could do better if it separated and tried to become an independent member state of the European Union.
"Five years ago I was in favor of a federal model with Spain, but now we have seen that is not viable," said Miquel Angel Aragon, a 37-year-old aid worker. "I am in favor of independence."
Catalonia is responsible for around a fifth of Spain's economic output and many residents feel central government gives back too little in recognition of the region's contribution.
Catalans have said in growing public protests that their industrialized region is being hit harder than most by austerity measures aimed at avoiding a national bailout like those needed by Greece, Ireland, Portugal, and Cyprus.