Dozens of people have been killed in a prison riot in the Venezuelan city of Barquisimeto.

Vice President Nicolas Maduro called the violence tragic and said the authorities had launched an investigation.

However, he did not give a death toll from the riot at Uribana prison.

The newspaper Ultimas Noticias reported on its website that 54 people were killed.

The television channel Globovision reported at least 50 killed and about 90 injured.

Both cited Ruy Medina, the director of Central Hospital in the city.

Penitentiary Service Minister Iris Varela said earlier that the riot broke out when groups of inmates attacked national guard troops who were attempting to carry out an inspection.

Ms Varela said the violence had affected a number of prisoners and officials, but said the authorities would hold off until control had been re-established at the prison to confirm the toll.

She said the government decided to send troops to search the prison after receiving reports of clashes between groups of inmates during the past two days.

Uribana prison was built to hold up to 850 inmates but currently has about 1,400, according to the Venezuelan Prisons Observatory, a watchdog group.

Meanwhile, Venezuelan President Hugo Chavez has overcome a serious respiratory infection, but is still being treated for breathing problems after cancer surgery last month, Information Minister Ernesto Villegas has told reporters in Chile.

Mr Chavez has not been seen in public since he underwent his fourth and most serious cancer operation in Cuba on 11 December.