Violence broke out when police tried to disperse thousands of members of the Islamic Movement in Nigeria (IMN) who were marching from Kano to Kaduna for the Ashura religious festival.
"The police arrived and started firing teargas canisters on the procession of Shiites to disperse them," grocer Ilyasu Ammani told AFP.
"I saw 15 bodies sprawled on the ground before the police evacuated them," said Ammani of the violence in Kwanar Dawaki, an area on the outskirts of Kano.
Witness Kabiru Mudassir said he saw more than "10 bodies being taken away in a police van."
Mudassir, who was on his way to work when he was caught in the fighting, said "more policemen are being deployed and a military jet keeps circling the area."
Nigerian police said they opened fire on the crowd after one of their officers was hurt.
"They injured one of our officers and our men opened fire because they were becoming violent," said a police officer who asked to remain anonymous.