Treasure hunters off Florida have found $4.5 million in gold coins from a Spanish ship that sank during a hurricane in the 18th century, the salvage company said on Wednesday.

Ten galleons traveling from Havana to Spain went down off Florida's east coast, not far from Vero Beach, in the July 1715 storm. The vessel broke up, and the booty was flung far and wide.

Brent Brisben, the head of 1715 Fleet - Queens Jewels, said in a Facebook posting that more than 350 gold coins, including nine Royals, had been recovered from the wreck on July 30 and 31, noting that the discovery occurred on the 300th anniversary of the wreck.

It was the second major find by the treasure hunters in recent months. In June, they found about 50 coins worth a total of around $1 million.

The latest coins found are extremely rare and are worth about $300,000 each, Brisben said.

"These Royals are perfect specimens of coinage of the time and they were made on royal order for the king of Spain," he explained.

And "we work extremely close to shore, which is surprising to most people", he said.

"These shipwrecks were pushed by the hurricane into the outer edge of the reef and then they were utterly destroyed by the wave action, so pieces of these ships have floated for miles all the way into the beach up into the dunes."

Under US state law, Florida gets 20 percent of the returns on treasure found off its coasts.