SAN JUAN, Puerto Rico (AP) -- Hurricane Gonzalo churned up heavy surf across much of the Caribbean on Tuesday and forecasters said it could pick up strength and become a major storm as it approaches Bermuda.

Authorities in the eastern Caribbean were searching Tuesday for seven boaters believed to have been lost in the storm.

Gonzalo was a strong Category 2 hurricane on Tuesday with top sustained winds of nearly 110 mph (175 kph) as it moved away from the U.S. and British Virgin Islands, according to the U.S. National Hurricane Center in Miami. Still intensifying, Gonzalo was centered about 830 miles (1,335 kilometers) south of Bermuda and moving northwest at 13 mph (20 kph).

The storm was expected to take a north-northwest turn late Wednesday and move over open waters toward Bermuda through Friday.

Forecasts said it was likely to intensify and possibly become a Category 4 hurricane by Thursday. Category 4 storms have sustained winds of at least 130 mph (209 kph) with the potential to cause catastrophic damage.

"Folks in Bermuda are going to need to start paying attention to this thing," Dennis Feltgen, a National Hurricane Center meteorologist, said by phone.

Forecasters might begin issuing storm watches Wednesday if Gonzalo is expected to impact Bermuda, he said.

The government in Martinique said Tuesday that rescuers were looking for five people believed to be aboard boats that became adrift or ran aground during the hurricane, as well as two other people who reportedly fell overboard.

A statement said authorities on islands including Guadeloupe and St. Maarten were helping with the search. It was unclear where exactly the people reportedly went missing, and how many boats are involved. Martinique spokeswoman Audrey Hamann did not immediately respond to a request for comment.

Gonzalo forced Puerto Rico-based Seaborne Airlines to cancel several flights in the region Tuesday. Hundreds of people were left without power along the north coast of the island.

Hazardous surf was forecast for Puerto Rico, the U.S. and British Virgin Islands, the Turks and Caicos Islands and the southeastern and central Bahamas.

Gonzalo passed just northeast of the British Virgin Islands overnight but did not cause any damage or flooding, Lorenzo Thomas, with the island's Department of Disaster Management, said by phone. Officials in the tiny territory of roughly 30,000 people had earlier shut airports, schools and government offices ahead of the storm.

Yvonne Remington, owner of the Hummingbird House bed and breakfast in Tortola, the largest of the British Virgin Islands, said she secured her outdoor tables and chairs but was perplexed about the lack of heavy rains and winds.

"I just turned on the weather channel to see where it went," she said in a phone interview early Tuesday. "We've had a bit of rain, and that's all."

Jim Woods, manager of the Manual Reef Marina in Tortola, said crews were busy Monday tying up the approximately 50 boats before heading home to await the storm. No damage was reported this morning, he said.

"There's just a lot of leaves floating around," he said.

Officials in the neighboring three-island territory of the U.S. Virgin Islands had shut seaports and the international airport on St. Thomas, but announced that schools and government offices would open on Tuesday.

Gonzalo pummeled Antigua on Monday as a tropical storm, tearing off roofs, uprooting trees and knocking out power, with crews working overnight with flashlights to help restore power. About a dozen people were treated at a hospital for light injuries including lacerations, which occurred because they were outside during the storm, said Sherrod James, deputy director of the National Office of Disaster Services.

Schools in Antigua remained closed on Tuesday, but the airport, government offices and other businesses were open, with people already waiting at bus stops in the morning.

Over the weekend, Tropical Storm Fay knocked out power to thousands in Bermuda before moving out over open ocean.

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