Hurricane Gonzalo gained strength in the Atlantic Thursday as it barreled toward Bermuda, which was bracing for a hit from the powerful Category Four storm.

Gonzalo's winds were whirling at 145 miles (233 kilometers) per hour, with even stronger gusts, taking it back up a notch on the five-point Saffir-Simpson scale, the US National Hurricane Center said.

It was expected to pass Friday near Bermuda, which could see flooding along the coast. Gonzalo, which has already killed one person in the Caribbean, triggered a hurricane warning for the British overseas territory.

Forecasters urged people in Bermuda to prepare for the expected arrival of the storm as it neared the archipelago.

"Preparations to protect life and property should be rushed to completion today," the NHC said.

Bermuda Premier Michael Dunkley said government offices and schools would be closed Friday in the grouping of islands home to about 60,000 people.

"It is important that these advisories are taken seriously and preparations made in good time which will help to reduce property damage and the likelihood of injuries or loss of life," Dunkley said.

"We have weathered storms before and we are well versed in how to manage our homes and our property. However, I urge people to err on the side of safety every time."

The international airport was expected to shutter from late Thursday until at least Saturday.

At 1800 GMT, the storm was located about 460 miles (740 kilometers) south-southwest of Bermuda. It was moving north at seven miles (11 kilometers) per hour, according to the Miami-based NHC.

"This general motion is expected to continue today," the NHC said.

"A turn toward the north-northeast and an increase in forward speed are expected tonight and Friday."

- 'Dangerous hurricane' -

The forecasters stressed that major hurricanes like Gonzalo tend to fluctuate in strength.

The storm could weaken later Thursday and on Friday, but Gonzalo is on track to be a "dangerous hurricane" when it moves near Bermuda, the NHC said.

The NHC noted that elevated and hilly terrain could face especially strong winds, since wind speeds atop and on the windward sides can often be up to 30 percent stronger than at the surface.

"A dangerous and life-threatening storm surge is expected to produce significant coastal flooding in Bermuda," the NHC said.

"Near the coast, the surge will be accompanied by large and destructive waves."

Bermuda Weather Service director Kimberley Zuill said Gonzalo would be "a long duration system" that will impact Bermuda with severe weather for about 27 straight hours, according to comments reported by The Royal Gazette newspaper in its online edition.

Gonzalo's only known victim so far was an octogenarian sailor killed in the Dutch territory of St Maarten.

Three people were reported missing in the adjacent French territory of St Martin and on the island of St Barthelemy after the storm passed, and French authorities expressed concern about four other people they were trying to contact.

The storm caused property damage on both islands, which were battered by strong winds and heavy rains.

Up to six inches (15 centimeters) of rain were expected over Bermuda.

Large swells triggered by Gonzalo were already affecting parts of the Virgin Islands, the northern coast of Puerto Rico and the Dominican Republic, as well as portions of the Bahamas.

Swells were expected to reach much of the US East Coast and Bermuda later Thursday.

Gonzalo is the seventh storm of the Atlantic season -- which stretches from June to November -- and the third hurricane to slam the Caribbean this year.

Hurricane Cristobal left at least four people dead in late August when it thrashed the Bahamas, Turks and Caicos Islands and Dominican Republic with heavy rains causing serious flooding.

The NHC predicted that storm activity will be lower than average this year.