Sanchez had launched her new site Wednesday morning, promising to offer Cubans "a complete spectrum of news, opinion pieces and information" about life on the island.
She aimed to make her "14ymedio" site Cuba's first independent news outlet in 50 years.
But within hours, people in Cuba who tried to connect to it were redirected to another page, Yoanislandia.Com, filled with attacks on the prize-winning writer and pieces by pro-government bloggers.
The state has controlled all media since the early days of the 1959 revolution that brought Fidel Castro to power.
Sanchez quickly took to her Twitter page to inform readers.
"14ymedio is accessible on Cuba's networks. Hurry net users before the next block," she wrote.
The unblocking of the site came hours after state-run newspaper Granma yesterday accused the United States of giving "full support" to the new newspaper, and noting that Cuba "will not tolerate any subversive activity."
Granma claimed "14ymedio" was fully funded by foreign sources and aimed to "feed the disinformation and defamation campaigns against Cuba."
Sanchez assembled a newsroom of 11 journalists, including herself, in Havana to produce the news site. Her husband, Reinaldo Escobar, is editor-in-chief.
Sanchez has said that the newspaper would also be distributed via cellphone and email, as well as through digital memory devices like USB flash drives, DVDs and CDs.
