Nigeria's northern Kano state issued a 24-hour curfew after a tribunal annulled an opposition candidate's election as governor and pronounced a member of President Bola Tinubu's party the real winner.
In a statement, police in Kano, which has the biggest number of registered voters, said curfew violators "will be arrested and made to face the full wrath of the law."
Security personnel occupied main roadways in Kano, Nigeria's capital, before the electoral tribunal verdict.
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Governors exercise considerable power in Nigeria, preside over budgets larger than those of some small African countries, and their backing frequently impacts who becomes president.
The decision by a panel of five judges on Wednesday triggered worries of turmoil in the country's largely Muslim state.
In the March gubernatorial election, Abba Yusuf of the New Nigerian Peoples Party, a regional party, defeated incumbent All Progressives Congress party candidate Nasiru Gawuna, who claimed fraud.
Yusuf has the right to challenge the tribunal's ruling to the Supreme Court. In Nigeria, where state governments preside over 36 states, it is fairly uncommon for governorship election results to be overturned.
