For those who took part in the referendum, the backing for Puerto Rico to become a US state was overwhelming. But only 23 percent of the island's 2.2 million voters turned out.
Opposition parties had supported the status quo and urged a boycott of Sunday's non-binding poll.
Results showed that 97.2 percent of those who did vote wanted statehood, 1.5 percent supported independence and 1.3 percent backed no change.
"We will go before international forums to defend the argument of the importance of Puerto Rico being the first Hispanic state in the United States," Governor Ricardo Rossello (photo) said after the result.
The non-binding plebiscite was pushed by the island's 38-year-old governor who came to power in January. Rossello said that, despite the economic crisis, the referendum could not wait. An unincorporated US territory under American control since 1898, Puerto Rico has no sovereign powers. It faces a public debt of $73 billion (65.2 billion euros) and its economy is in stagnation.
Over the past several days the governor has repeated, during a series of interviews and on Twitter, that "the moment to vote for the decolonization has arrived!" He ran on a campaign promise to end the long "colonial" relationship with the US, and make the island the 51st state of the USA.
The island's status is "fundamental" to breaking free from economic turmoil, said Christian Sobrino, chief economic adviser to the government.
"It is because Puerto Rico is in an unequal relationship" with the US government that the bankrupt island's finances are now under a largely US-appointed control board, he said.
Puerto Rico was a Spanish colony that was taken over by the US at the end of the 19th century. Since 1952, it has enjoyed broad political autonomy as a commonwealth or "free associated state."
As American citizens Puerto Ricans can freely enter the US mainland but don't have the right to vote for US presidents or elect representatives to Congress, even though US lawmakers have the ultimate say over the territory's affairs.
Many blame Washington
Many Puerto Ricans attribute the economic plight plaguing the island to Washington's power over them.
For decades the island territory enjoyed a US federal tax exemption that attracted many American companies to set up shop. But those breaks were ended in 2006, prompting firms to leave the island en masse.
Unable to counter the massive loss in revenues and the global financial crisis, the island plunged into recession.
But the so-called "Caribbean Greece" found that US municipal bond markets were an easy way to kick the proverbial can down the road. Investors got attractive tax-exempt bonds that provided ready cash but sank the island deeper into debt.
"Public opinion is divided," said Edwin Melendez, director of the Puerto Rican Studies Center at the City University of New York. "Half the population, or more, believes that nothing will happen."
"The US government has no obligation to pay attention to the result," he said, arguing that it will "lack legitimacy" if a significant part of the electorate abstains.
bik/jm (AFP, dpa)