Beijing has also blocked the websites of the UK newspaper The Guardian, and France's Le Monde along with the home page of the International Consortium of Investigative Journalists (ICIJ).
China flicked the switch on the sites after they published leaked information revealing that over a dozen family members of high-ranking Chinese politicians have offshore companies based in the British Virgin Islands.
Among those fingered by the left-leaning El País is Wen Yunsong, the son of former premier Wen Jiabao. Yunsong, a venture capitalist, who is currently chairman of a state-owned satellite services company.
Consultancy firm PriceWaterhouseCoopers and Swiss banks Credit Suisse and UBS are also named in the documents as middlemen in the Chinese business deals.
The financial documents from the Virgin Islands have come to light as part of a two-year ICIJ investigation into the offshore assets of China's elites.
The ICIJ then shared those documents with newspapers including El País.
Diplomatic relations between China and Spain have been tense in recent times.
In November, a Spanish judge authorized the arrest of former Chinese President Jiang Zemin and four officials in an investigation into the alleged genocide of Tibetans in the 1980s and 1990s.
China's foreign ministry spokesman Hong Lei went on to seek a "clarification" saying he hoped the Spanish authorities wouldn't do things "that harm the Chinese side and the relationship between China and Spain".
In another recent incident, China's embassy in Spain demanded an apology from Spanish TV channel Telecinco after a 'vulgar' and 'insulting' comedy sketch was aired during the broadcaster's New Year Gala, causing anger across the Asian superpower.