At least 16 people died and 78 were injured when a float hit power lines in the Haitian capital Port-au-Prince, on the second day of an annual festival.

The float caught fire after it hit a high-voltage overhead power cable, witnesses said.

Video of the incident appeared to show the electric cable catch the head of a singer from popular Haitian hip-hop band Barikad Crew.

The rap group's star singer, who goes by the name Fantom, was struck directly by the fallen cable and is in a critical condition, the website Haiti Press Network said.

Seven people were reported dead on the float, and others were killed in the ensuing panic.

Many of those who died were dancers and musicians on the float.

Thousands of people have joined a memorial march to pay their respects to the victims.

Local television showed Haitian president Michel Martelly leading mourners in a 'parade in white', walking through the same streets where the carnival event was held the previous day.

The president lit candles on a white cake in memory of the victims.

It marks the beginning of three days of national mourning, with flags to be flown at half-mast on all public buildings.

National funerals will be held on Saturday.

Sorry, this video has expired Chaotic scenes after fatal carnival accident

The Haitian government said the accident happened near the city centre on the Champ de Mars at around 2:48am (local time), on the second day of the carnival as tens of thousands of people watched.

Authorities cancelled the third and last day of the Carnival celebrations on Tuesday, and declared three days of mourning.

Haitian president Michel Martelly expressed his "sincerest sympathies" to the victims in a Twitter message.

"The government sends its condolences to the families of the victims and stands ready to assist everyone affected by this tragedy," communications minister Rotchild Francois said in a statement.

Up to 100 people gathered at the morgue of the Hospital General to see if family members had been brought there.

Prime minister Evans Paul called on Haitians to pay homage to the dead by dressing in white and marching silently at the Champ de Mars, the parade ground where the accident occurred.

The raucous three-day annual street parade coincides with other Mardi Gras carnivals around the world and attracts large night-time crowds eager to witness competing music bands atop highly decorated floats.

It is not the first time tragedy has struck the Barikad Crew.

Three members of the group were killed in a car accident in 2008, while another member died in the January 2010 earthquake in Haiti, according to reports.

At Brazil's carnival, three men were electrocuted when they pushed a float toward a parade ground and it struck a high-tension power cable in the Nova Iguacu suburb of Rio de Janeiro, police said.

A sun on the float made of wire touched the power line and sent a fatal electrical charge through the metal frame of the decorated platform, police said.

Authorities cancelled carnival festivities in the district after the accident.

A woman cries following the tragedy in Port-au-Prince. ( Reuters: Andres Martinez Casares )

Reuters/AFP