A United States flag flutters in the wind off of a Statue of Liberty Island ferry boat in lower Manhattan in New York April 24, 2015. The Statue of Liberty is seen in the distance. [Photo/Agencies]

NEW YORK - The Statue of Liberty was declared safe on Friday after a bomb scare forced the evacuation of thousands of tourists from the New York Harbor landmark, the National Parks Service said.

All visitors and staff were safely ferried off Liberty Island soon after an anonymous caller threatened to blow up the statue that stands guard at the mouth of the Hudson River, Mindi Rambo, a National Park Service spokeswoman, said in a statement. The 911 call came in at around 11 am local time.

About four hours later authorities sounded the all-clear after a security sweep, including two canine patrols, failed to uncover any explosive device on the island.

Liberty Island, which draws some 4 million visitors a year, will reopen on Saturday, the park service said.

Statue Cruises, which operates ferry service between Liberty Island and Battery Park at the southern tip of Manhattan, said it took about 2,700 people off the island and offered passengers full refunds.

"We are working with NPS to reunite passengers with their belongings left behind as a result of today's events," Mike Burke, vice-president of Statue Cruises, said in a statement.

Sue Rodgers, 45, and her daughter Rebekka Rodgers, 16, were among those who left personal property behind.

The Australian tourists said they were told the evacuation was underway soon after they had climbed to Lady Liberty's crown, the highest point of the 305-foot statue open to the public.

"We got our pictures," the mother said with a laugh while sitting in Battery Park in the chilly April sunshine. "It was all very calm."

The Statue of Liberty, a gift to the United States from the people of France, was formally opened in 1886. The colossal torch-bearing figure was closed for nearly eight months due to damage to the island by Superstorm Sandy in 2012.