A massive fire in South Africa's houses of parliament in Cape Town caused the roof of the old National Assembly building to collapse on Sunday as the blaze continued to rage all day.

No casualties have been reported in the fire, which has also spread to the wing housing the current National Assembly, where parliament sits.

“The roof of the Old Assembly building has collapsed and is gone,” Jean-Pierre Smith, Cape Town's mayoral committee member for safety and security, told reporters.

The cause of the fire was not yet known, but an investigation was opened.

President Cyril Ramaphosa told reporters at the scene an arrest had been made.

“Someone has been held right now and is being questioned,” he said.

The historic building houses a collection of rare books and the original copy of the former Afrikaans national anthem “Die Stem Suid-Afrika” ( “The Voice of South Africa “), which was already damaged.

“The entire building has suffered extensive smoke and water damage,” Smith said, adding that “the fire has not been contained”.

It started at around 03:00 GMT on Sunday in the parliament complex's oldest wing, which was completed in 1884 and has rooms covered in wood where parliamentarians once sat.

It then spread to newer parts of the complex which are currently in use.

“Firefighters are currently trying to control the fire in the New Wing, where the fire has affected the National Assembly Chamber,” parliamentary spokesman Moloto Mothapo told an online press conference.

The imposing red and white building was still shrouded in a thick cloud of black at midday.

Metres from Tutu's burial

A team of firefighters who were first to arrive at the scene battled the flames for several hours before being forced to retreat and call for reinforcements.

Some 70 firefighters were later deployed, some using a crane to spray water on the blaze.

Former Cape Town mayor and current minister Patricia de Lille warned it would still be several hours before the fire was brought under control.

Inside the rooms, fine showers of grey ash fell from the ceiling to the floor, which was already littered with debris.

Emergency services feared the fire could spread swiftly through the old rooms, which are decorated with wood, thick carpets and curtains.

Images broadcast on television had earlier shows giant flames leaping from the roof.

The area around the fire in the upmarket neighbourhood was quickly cordoned off.

The cordon stretched to a square where flowers were still displayed in front of the nearby St George's Cathedral, where anti-apartheid icon Archbishop Desmond Tutu's funeral took place on Saturday.

After a simple, no-frills mass, with a cheap coffin — according to the famously modest Tutu's instructions — his ashes were interred in the cathedral on Sunday.

Second fire in a year

Cape Town has been home to South Africa's houses of parliament since 1910, when separate administrations formed a union under British dominion and became a predecessor to the modern South African republic.

The site includes the National Assembly and the upper house National Council of Provinces, while the government is based in Pretoria.

It was in parliament where South Africa's last apartheid president FW de Klerk announced in 1990 plans to dismantle the brutal white-minority regime.

The houses of parliament in Cape Town consist of three sections, with the newer additions constructed in the 1920s and 1980s.

Another fire also broke out in the older wings of parliament in March, but it was quickly contained.

Cape Town suffered another major fire in April, when a blaze on the famed Table Mountain which overlooks the city spread, ravaging part of The University of Cape Town's library holding a unique collection of African archives.