Nineteen people were killed in Cairo on Sunday when Christians protesting against an attack on a church clashed with police, state television said.

Protesters threw rocks and petrol bombs at police, and set fire to vehicles as thick smoke wafted through the street, witnesses said, in some of the most violent scenes since an uprising overthrew former President Hosni Mubarak in February.

The clashes began when some protesters threw stones at army troops guarding the television building. Several cars and buses were set on fire.

Hundreds - mostly Christian - were demonstrating in protest at the destruction of a church in the southern Egyptian province of Aswan.

State television and radio employees were trapped inside the building after the army closed all doors and prevented anyone from leaving, witnesses told dpa.

Several roads around the area were closed by protesters, who were preventing cars from passing.

During the protest, led by several bishops, the demonstrators burnt photos of the governor of Aswan, Mustafa al-Sayed, who had said that the church in the village of Marinap had been built illegally.

The protesters demanded the governor be sacked and the church rebuilt.

In the southern city of Luxor, a group of protesters briefly blocked the city's main roads. However, the governor convinced them to leave after promising to resolve the issue of the destroyed church.

Christians account for around 10 per cent of Egypt's 80-million-strong population. Tensions are not uncommon between them and the country's Muslim majority.

In March, 13 people were killed in sectarian clashes around the Cairo neighborhood of Manshiyet Nasser, shortly after a church was torched in the village of Sol, south of the capital.