Puerto Rico wants to become the 51st state of the US
Voters in Puerto Rico have supported a non-binding referendum to become a full US state.
The measure will require approval from the US Congress, but President Barack Obama has said he will respect the vote.
The island is currently a US territory, which uses the dollar and whose citizens travel on US passports.
But it does not return senators to the US Congress and is represented in Washington by a non-voting delegate.
Almost 80% of the island's electorate took part in the referendum, the fourth in the past 45 years.
With almost all the votes counted, almost 54% voted to change the island's relationship with the US.
And in reply to a second question on what future they favoured, nearly two-thirds wanted full statehood.
If Congress grants its approval, Puerto Ricans would have the right to vote in all US elections, but would also have to pay federal taxes, something at present they are excused from.
The island came under US control in 1898 when Spain lost the island at the end of the Spanish-American war.
Ties were strengthened in 1917 when Puerto Ricans became US citizens and were allowed to serve in the military.
'No other option'
There are now almost a million more Puerto Ricans in the US than on the island.
Supreme Court judge Sonia Sotomayor, singer Jennifer Lopez and the former jazz musician Tito Puente are all of Puerto Rican descent, though all three were born in New York.
Ties between the island and the mainland are strong and many on the island considered it inevitable that a full union be requested.
A young voter in the capital San Juan, Jerome Lefebre, said: "Puerto Rico has to be a state. There is no other option.
"We're doing okay, but we could do better. We would receive more benefits, a lot more financial help."
But that opinion was rejected by Ramon Lopez de Azua: "Puerto Rico's problem is not its political status.
"I think that the United States is the best country in the world, but I am Puerto Rican first."
The island has been hit hard by the current recession - it has debts of $68bn (£42bn) and unemployment is more than 13%.
President Barack Obama, who visited the island last year, has said he will respect the will of Puerto Ricans if there is a clear majority.
Any change would require approval by the US Congress.