Cape Town, Jan 3 (IANS): The interior of South Africa's National Assembly, the lower house of Parliament, was "extensively destroyed" by a fire, a local official said on Monday.

As of 6.50 a.m. (local time) Monday, firefighters have been working at the fourth floor of the National Assembly building, which is still smouldering, Xinhua news agency quoted Jean-Pierre Smith, Cape Town's mayoral committee member for Safety and Security, as saying.

The fire, which erupted on Sunday, has affected both the Old Assembly Wing and the National Assembly Wing Parliament, which also houses the upper house, National Council of Provinces.

The blaze at the rest of the building has been brought under control and the number of firefighters has been reduced from 20 to 10, he said, adding that he hopes the fire would be put out over the next two to three hours.

No one is injured, he said.

The cause of the fire is still unknown, while one person has been arrested in connection with the fire.

Initial reports indicated that the fire started at the hall of the Old Assembly building, then spread to the National Assembly, President Cyril Ramaphosa told reporters.

He promised an extensive investigation into the fire when visiting the scene.

"We need to go a lot deeper, a lot deeper into how this type of event can take place and what measures we will need to take going forward," he said.