President Macky Sall announced on Saturday the vote would be delayed to an unspecified date due to a dispute over the candidate list - a move some opposition and civil society groups have denounced as an "institutional coup".
In an early sign of pushback against the postponement on the streets, groups of protesters blocked traffic at various points along a main thoroughfare in Dakar with makeshift barricades of burning tyres.
In one area, around 200 people retreated into side streets after police in riot gear fired tear gas and started detaining protesters.
At least two opposition presidential candidates were swept up in the melee. In an online post, candidate Daouda Ndiaye said he was attacked by police, and the campaign manager of Anta Babacar Ngom told Reuters she had been detained by security forces.
Former prime minister Aminata Toure also said she had been detained and taken to a police station in Dakar as soon as she got out of her vehicle.
"President Macky's exit slip is now marked with the seal of this unprecedented democratic regression," Toure posted on Saturday in response to the postponement.
The police did not immediately reply to a request for comment.
Further protests are planned outside parliament on Monday.
Senegal has never delayed a presidential vote and uncertainty about what happens next threatens to fuel further unrest like the deadly protests of recent years that have tarnished its reputation as one of West Africa's most stable democracies.
After Sall's televised announcement, the Economic Community of West African States (ECOWAS) expressed concern about the circumstances that led to the postponement and called for a new election date to be set quickly.
The French foreign ministry on Sunday also urged the authorities "to remove the uncertainty surrounding the electoral timetable, so that the elections can be held as soon as possible and in compliance with the rules of Senegalese democracy".
(Additional reporting by Zohra Bensemra, Ngouda Dione in Dakar, Felix Onuah in Abuja, Michel Rose in ParisWriting by Alessandra Prentice; Editing by Giles Elgood)
By Cooper Inveen and Diadie Ba
