Grand Bahama and Abaco were among the worst-hit by Hurricane Dorian. (AFP)

The devastated northern Bahama islands were facing a fresh tropical storm on Saturday, potentially complicating desperately needed relief efforts to the shattered archipelago in the wake of Hurricane Dorian.

The announcement from the National Hurricane Centre (NHC) came after it had warned early Friday that a strengthening tropical depression was heading for the same islands hit by Dorian last week.

The storm, dubbed Humberto, is expected to strengthen into a hurricane, moving very near the northwestern Bahamas on Saturday, before shifting to offshore Florida after the weekend, the Miami-based forecaster said.

Grand Bahama and Abaco -- in the path of the strengthening weather system, according to Bahamian forecasters -- were among the worst-hit by Dorian.

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

"The weather system will slow down logistics," Smith told a press conference in Nassau, the capital. "Fuel and water remain the biggest needs in Abaco."

Humberto was generating 40 mile (64 kilometer) per hour winds, the NHC said, and was expected to become a hurricane in two or three days.

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 the Department of Meteorology's director Trevor Basden.

The announcement that yet another storm would lash the Bahamas came as UN Secretary General Antonio Guterres warned of the dangers of climate change during a visit to the hurricane-battered archipelago.

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

He said 75 percent of all buildings had been destroyed in some areas by Dorian, a Category 5 storm.

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

He said the hurricane demonstrated the need to address climate change.

"In our new era of climate crisis, hurricanes and storms are turbo-charged," Guterres said. "They happen with greater intensity and frequency -- a direct result of warmer oceans.

"Science is telling us: this is just the start. Without urgent action, climate disruption is only going to get worse. Every week brings news of climate-related devastation."

Meanwhile, NEMA raised the death toll from 50 to 52 -- although officials have said they expect it to rise significantly.

Former prime minister Hubert Ingraham said earlier this week he feared the final death toll could be in the hundreds.

NEMA spokesman Smith said some 1,300 people remain unaccounted for.

He said 71 people were staying in shelters on Grand Bahama island and 2,037 in shelters in New Providence, where Nassau is located.