A freak storm has blasted through Haiti's capital, killing at least five earthquake survivors as it tore down trees, billboards and tent homes, authorities said.

Three adults and two children were killed in the tarp, tent and shack camps that still dominate Port-au-Prince more than eight months after the January 12 earthquake, civil protection head Marie Alta Jean-Baptiste told the Associated Press. Several more were injured.

"We are investigating to see how many tents and camps were damaged," Ms Jean-Baptiste said.

The storm passed through the mountain-ringed bowl of the Haitian capital, exposing rubble-filled neighbourhoods to wind and rain at levels far below a sustained tropical storm. But that was enough to provoke panic and chaos, especially in encampments still home to more than 1.3 million people.

Gales sent tarps and poles flying, threw tin roofs into the sky and opened family shacks to falling rain. Wind rattled walls and windows of standing buildings with a clamour reminiscent of the quake itself.

"It was just a storm. Just a wind put us in a corner!" said Bresil Vignion, standing in the wreckage of his family's tin shack in a camp along the Canape-Vert road. "Tonight we don't know where we are going to sleep."

Reports of storm damage and deaths were slow to filter in as mobile phone reception remained degraded hours after the storm passed.

The sudden storm was not associated with any tropical system, Michael Lowry of the US National Hurricane Centre told AP. Meteorologists saw only a low-pressure system move across the Greater Antilles.

But for those living in this ravaged city, where reconstruction has barely begun, it was a forceful reminder of the danger still posed to a vulnerable country by an active Atlantic hurricane season months from being over.

"After what happened today, we hope we don't get a second one like it," said Patricia Pierre-Saint, a 47-year-old phone-card vendor who lost her home, child and husband in the quake.