More than 1,000 people on average are arriving every day in Cuba from the United States, most of Cuban origin. This makes Havana's long-time foe its second source of visitors after Canada, travel industry and diplomatic sources told Reuters.

US charter companies flying to the Communist-ruled island say business has boomed since President Barack Obama's administration lifted restrictions last year on Cuban-Americans visiting their homeland, and also loosened curbs on academic, religious, cultural and other professional travel.

US citizens are forbidden from travelling to Cuba without their government's permission under a wide-ranging US trade embargo on the island imposed nearly five decades ago.

"There is a huge increase this year compared with 2015," said Armando Garcia, president of Marazul Charters, the oldest of a growing number of companies chartering flights to Cuba.

More Americans are also arriving to Cuba through third countries such as the Bahamas.

There are no regular scheduled commercial flights between Cuba and the United States which lie less than an hour's flight apart, separated by the Florida Straits.

"We estimate the total (visitors from the US to Cuba) for the year will be more than 400,000," a US State Department source told Reuters.

Cuba reported 2.4 million tourists arrived , with Canada the largest provider at close to 915,000, followed by Great Britain at 172,000 and Spain at 129,000.

Marazul's Garcia estimated US travel to Cuba would increase another 30 percent in 2017.