A tropical storm warning was issued on Friday for the northern Bahamas as UN Secretary General Anthony Guterres visited the hurricane-battered islands.

The Miami-based National Hurricane Center said a depression had formed near the Bahamas and was forecast to become a tropical storm on Saturday.

Bahamian meteorologists said the islands of Grand Bahama and Abaco, which were the worst-hit by category-5 Hurricane Dorian, were in the path of the approaching weather system.

Winds of up to 60 miles (100 kilometers) per hour were expected and heavy rainfall could bring some flooding to the already saturated islands, said Trevor Basden, director of the Department of Meteorology.

Carl Smith, a spokesman for the Bahamian National Emergency Management Agency (NEMA), said the storm could have an impact on relief and recovery efforts on Grand Bahama and Abaco.

"The weather system will slow down logistics," said Smith, adding that fuel and water remain in biggest needs in Abaco.

UN chief Guterres said in a tweet that he had come to the Bahamas "to express my solidarity with the Bahamian people" and "ways we can continue supporting them."

Seventy-five percent of all buildings had been destroyed in some areas by Dorian, a Category 5 storm, said Guterres.

"Hospitals are either in ruins, or overwhelmed," he said. "Schools have been turned into rubble. Thousands of people will continue to need help with food, water and shelter."

Meanwhile, NEMA raised the death toll from Hurricane Dorian to 52 from 50,  although officials have said they expect it to rise significantly once all the bodies are recovered.

Some 1,300 people remain unaccounted for following Hurricane Dorian, said Smith.