WILLEMSTAD, Curacao – Masked men in jackets emblazoned with the word “police” boarded a fishing boat Friday in Curacao and stole 70 gold bars worth an estimated $11.5 million, officials in the southern Caribbean island said.

The boat’s captain was struck in the head in the early-morning assault before the thieves made off with the gold in three cars, police spokesman Reggie Huggins said. Authorities believe there were at least six men involved in the heist. No suspects were in custody.

Huggins declined to say who owned the approximately 476 pounds of gold but he said it was a legal shipment that was being trans-shipped through Curacao and officials in the island had been advised in advance that it was coming as part of normal security protocols. He declined to disclose the eventual destination of the metal.

“Authorities knew of the shipment because the official procedure was followed,” the spokesman said.

Huggins said that guards to the port area let the assailants inside a restricted area in the mistaken belief that they were customs officials. The men’s jackets had the word “police” in English but in Curacao the word would be written in Papiamento, one of the island’s three official languages, as “polis.” During the robbery, crew members said they wore hoods and masks and made off with the gold in a matter of minutes.

“The crew said it was like a movie operation, very fast,” Huggins said.

The captain and three crew members were from the South American country of Guyana, he said.

The boat, by its appearance, would seem an unlikely place to stash that amount of gold. The “Summer Bliss” is a fishing boat with rust streaks on its white cabin and no visible security.

A crew member who gave his name as Raymond Emmanuel told The Associated Press that they left Guyana four days ago and arrived early Friday in Curacao. Contradicting police, he said they were delivering the gold to a company in Curacao but said he did not know the name of the business.

He referred questions about the source of the gold to the captain, who was meeting with authorities on the Dutch Caribbean island and not immediately available.

Emmanuel said the gold was locked away when the thieves boarded the vessel. “They took everything,” he said.

The crew member said neither he nor anyone else on the vessel was armed. “This is normal,” he said. “We never carry arms. Since I started working here, I’ve transported gold once before, and this is the system.”

Colin Sparman, executive secretary of the Guyana Gold and Diamond Miners Association, said legal shipments are typically made by air under heavy security. But gold smuggling is common to avoid taxes and royalty payments on the precious metal.

Curacao, just north of Venezuela, is primarily known as tourist destination, particularly for divers. It is also an offshore financial center, especially for people from South America.

Associated Press writers Orlando Cuales in Willemstad and Bert Wilkinson in Georgetown, Guyana, contributed to this story.