A fire has gutted an iconic building at Uganda's Makerere University, which is a prominent landmark in the capital.

Known as the "Ivory Tower", an overnight blaze has left its distinctive white walls with blue-shuttered windows blackened.

Police in Kampala have started an investigation into the cause of the fire at one of Africa's oldest and most prestigious universities. The vice-chancellor described the destruction as unbelievable.

"It is a very dark morning for Makerere University. Our iconic Main Administration Building caught fire and the destruction is unbelievable. But we are determined to restore the building to its historic state in the shortest time possible," Vice-Chancellor Barnabas Nawangwe tweeted.

Fire officers fought the huge fire from around midnight, reports the BBC's Patience Atuhaire from Kampala.

Though most of it had been put out by early on Sunday afternoon, some parts of the building were still smouldering and smoke could still be seen, our reporter says.

Huge cracks can be seen on some of the outer walls, most of the roof has been burnt off and many of the windows are completely burnt out, she says.

Initial reports indicate that the fire may have started from the roof, spreading to floors that house the finance and records department.

A historian of East Africa, Derek Peterson, says the fire is a disaster for Uganda and for East Africa.

"The building holds student records, and the basement is full of archive files spanning the whole history of the institution," he tweeted, adding that he had been intending to help organise a project to catalogue the collection.

Makerere was first established in 1922 as a technical school and has grown into a widely respected university.

Its alumni include independence-era leaders such as Julius Nyerere of Tanzania, renowned writers including Kenya's Ngugi wa Thiong'o, academics and clergy like John Sentamu, the recently retired Anglican archbishop of York.