The US Coast Guard says it has intercepted almost 3,000 Cuban migrants off the Florida coast this year, the highest figure for more than a decade.
It says more Cubans are paying gangs to try to reach Florida on fast launches rather than using home-made rafts.
The US is starting a temporary visa programme for Cubans to cope with delays in issuing regular papers.
But experts say the situation is not comparable to a mass exodus from the island in 1994.
About 37,000 Cubans were arrested at sea that year in what became known as the "rafters' crisis".
As of Tuesday, the Coast Guard had intercepted 2,988 Cubans this year - surpassing the figure for 2005.
Coast Guard spokesman Luis Diaz said that - rather than reflecting a sharp rise in migration - the figures showed the US authorities were doing a more effective job.
"For us, this means that our units and the national security agencies are working harder and intercepting more migrants than in previous years," he told the BBC.
Washington currently allows 20,000 Cubans to join relatives in the US every year, but they experience long bureaucratic delays while waiting on the island.
The new system - which the US immigration service hopes will "discourage dangerous and irregular maritime migration" - means that successful applicants won't need full resident status before leaving for Florida.
The latest figures are causing controversy among Cuba watchers in the United States.
"There are obviously more rafters," said Omar Lopez, an exile from the Miami-based Cuban-American National Foundation.
"Cuban citizens are marginalised from political, economic and social life - so their only hope is to leave the country."
The Centre for Cuban and Cuban-American Studies at the University of Miami warned in a recent report that "a silent, but increasingly obvious new mass immigration from Castro's Cuba could be under way".
But Phil Peters of the Lexington Institute, a think-tank, said there was no evidence of an imminent crisis.
Experts say a key factor in migration from Cuba is Washington's so-called "Wet Foot, Dry Foot" policy.
This allows any Cuban who reaches US soil to stay in America, but means that most migrants intercepted at sea are sent back to the island.