Thousands of people have gathered outside the huge, ornate palace of the Sultan of Sokoto, waiting to pay their respects following his death in a plane crash on Sunday.
The BBC's Ardo Abdullah Hazzad says the whole city feels like a graveyard - offices, shops, banks and markets are all closed and are likely to remain so until Friday, when the period of mourning ends in the state.
The Sultan of Sokoto was widely respected
The crowds - young and old, rich and poor - wait patiently, some in tears, for their turn before entering the palace in small groups to meet the family of the late Sultan Muhammadu Maccido and other traditional rulers.
"To me this is a terrible event because I loved the sultan. May the Almighty give him peace," Liman Muhammadu, an elderly trader among the crowds told Reuters news agency.
President Olusegun Obasanjo paid his respects on Monday, along with a host of other dignitaries, including two former presidents.
The son of former President Shehu Shagari also died on the ADC Boeing 737, which crashed just after taking off from the capital, Abuja, on its way to Sokoto.
The sultan's son, Mohammed, one of his grandsons and another northern senator were other victims of the crash which has decimated northern Nigeria's elite.
The Sultan of Sokoto was the spiritual leader of Nigeria's 70m Muslims and Sultan Maccido was particularly well respected for his efforts to end conflict between Nigeria's Muslims and Christians.
He also tried to end a boycott of a polio vaccine by some northern Muslim clerics, which has set back efforts to eradicate the disease by several years.
SULTAN OF SOKOTO
Leads Nigeria's 70m Muslims
Sokoto base for 19th Century jihad, spreading Islam across northern Nigeria
Sokoto still Nigeria's centre for Islamic learning
Our reporter says the crowds of mourners are likely to remain outside the sultan's palace for many weeks - some travelling from neighbouring Niger and other West Africa countries with large Muslim populations, such as Chad, Mali and Senegal.
A group of seven traditional rulers, known as kingmakers, is to start drawing up a shortlist of candidates to become the next sultan, possible as early as Tuesday - if they can find time among the mourning and condolences.
There should be eight kingmakers but one of them also died in the crash.
The kingmakers are to present a list of three names to Sokoto State Governor Attahiru Bafarawa, who is to choose the new sultan over the next few days.
The name of the preferred candidate will come top of the list and the governor is expected to choose him.
When Sultan Maccido was overlooked despite coming top of the list in 1988, there were riots in the streets of Sokoto.
He was only later installed some years later.
After the appointment of the next sultan, the crowds outside the palace are likely to further increase, now mixing their condolences with congratulations.
The new sultan will be chosen from Sokoto's ruling dynasty - descendents of Uthman Dan Fodio, who launched a jihad, or holy war, in 1804, spreading Islam across northern Nigeria and its neighbours.
Dan Fodio, an ethnic Fulani Islamic scholar, rose up against the Hausa rulers of what is now northern Nigeria and Niger and created an empire which stretched from modern-day Burkina Faso to Cameroon, becoming one of Africa's largest pre-colonial states.
At its height, it took four months to travel from east to west and two months north to south.
Dan Fodio's son, Muhammed Bello, established the empire's capital in Sokoto and it has remained the centre of Nigerian Islam ever since, with its huge mosque opposite the sultan's palace.