A float in Rio de Janeiro's world famous carnival parade has crashed, injuring 12 people with at least one victim in a serious condition.

The incident involved the last float of the first samba school parading through Rio's Sambadrome, but organisers carried on with the show.

The float of samba school Paraiso de Tuiuti crashed into a fence that separates the stands from the pavement, injuring spectators and revellers.

Police began an investigation as soon as the float finished its journey through the Sambadrome.

Anna Maria Ciarlini, a medical co-ordinator at the Sambadrome, said most of the injuries were minor, but two people were rushed to a nearby hospital, one with severe head injuries.

She said a total of 12 people were injured but Brazilian media reports counted 20 people seeking medical attention.

The pavement was wet because of a persistent drizzle. Rain can make the big floats harder to guide.

The drizzle also created more difficulties for firefighters to cut through a fence to remove two women drenched in blood.

In a statement, Paraiso do Tuiuti said it "deeply regrets" the incident.

"Our board offers its deepest sentiments and is open to make any clarifications as soon as all the causes of the accident are investigated," it said.

"We will offer all the assistance to the victims of this irreparable incident."

Organisers tried to adjust, but then they lost control

Despite the incident, head of the Rio parade Elmo dos Santos said "the show must go on".

"The rain made the car veer to the left," he said. "Organisers tried to adjust, but then they lost control. It is all regrettable, but we cannot stop."

Reveller Elmano Santos, from Rio, said the float missed him by inches.

"It was very quick. I saw a few journalists taking pictures close to the float get injured," he said.

"I can't remember the last time I saw an accident here."

Paraiso do Tuiuti was the first of six samba schools parading in the night's extravaganza at the Sambadrome.

Police investigator William Lourenco Bezerra said the three conductors of the float would be questioned, adding that one driver had already been identified as the main focus of the probe.

"The last float went into reverse and ended up pressing revellers against the fence on one side," he said.

"That caused chaos. Then the conductors made a quick manoeuvre to the opposite direction and injured more people."

"The main conductor of the float mixed with the rest of the samba school and left. But he has already been identified and will be investigated."

Only revellers at the entrance of the Sambadrome were aware of the incident and many agreed with the decision to carry on.

"It is all very sad, but to stop Carnival would create an even bigger problem," said Jonas Elias, a tourist from Salvador.

Of course this spoils the party a bit, but to frustrate all this crowd would make the tragedy even bigger

"Of course this spoils the party a bit, but to frustrate all this crowd would make the tragedy even bigger."