(CNN) -- At least 17 people have died and dozens more were rescued after their boat capsized off the Turks and Caicos Islands in the Caribbean on Wednesday, according to the local government and U.S. officials.

The U.S. Coast Guard, assisting the islands' rescue crews, retrieved about 55 Haitians in waters 100 meters from shore, the U.S. agency said. They fell into the water when their overloaded sail freighter tipped over, the guard said.

The nationalities of the 17 dead people weren't immediately clear Wednesday, but 12 were males and five were female adults, said Colin Farquhar, commissioner of Royal Turks and Caicos Islands Police Force. Earlier reports had put the death toll at 18.

Farquhar added that the search for additional casualties concluded late Wednesday because of darkness and worsening seas. The search will resume Thursday, he said.

Although the Coast Guard put the number of rescued at near 55, local authorities used different numbers.

A total of 33 people -- 21 men including a child and 12 females -- were detained as suspected illegal Haitian migrants and "will be repatriated to Haiti at the earliest opportunity," Farquhar said.

Officials couldn't be immediately reached for comment to explain the discrepancy between the approximate 55 rescues the Coast Guard cited and the 33 detainees Farquhar discussed.

The Turks and Caicos Islands government said in a Facebook statement that a sailing vessel believed to be carrying suspected illegal migrants was intercepted by the Marine Branch of the islands' police force after 3 a.m. Wednesday. Two hours later, while the boat was being towed to a dock to unload the suspects, the sloop capsized, the statement said.

"The stricken vessel has now been removed from the water and will be central to our ongoing investigations into this matter," Farquhar said. "We must all remain vigilant to combat illegal migration."

He thanked police officers and emergency personnel for working under what he called "challenging circumstances."

Police were searching Wednesday "for the handful of people who reached shore and fled the scene," the government said.

The Turks and Caicos Islands are a British territory.

The incident occurred near the country's island of Providenciales, commonly known as "Provo" and described on the official tourism website as its most developed isle where most international flights arrive.

The 33 rescued people -- all Haitians -- were in custody of the government's immigration detention-removal center, Farquhar said. Authorities revised that figure from an earlier reported count of 32 rescued people.

Haitian migrants seeking to enter the United States have used the Turks and Caicos Islands and the Bahamas as way stations to enter the United States.

Migrants appear undeterred, even after deadly shipwrecks

CNN's Elwyn Lopez contributed to this report.