There have been labour tensions in a country where previous strikes led to dozens of deaths.
Unidentified assailants attacked a police station and demonstrators clashed with gendarmes in several districts of Conakry, witnesses said.
“By midday, these demonstrations had unfortunately caused the deaths of at least five people,'' the government said in a statement, calling the protest “illegal and forbidden''.
Government said that 30 people had been injured, including members of the security forces, and 12 arrested.
Witnesses said that three of the dead had been shot but it was not possible to verify that information.
General strikes about 10 years ago caused major disruptions in Guinea, which has around a third of the world's reserves of bauxite, used to make aluminium.
The subsequent crackdown led by security forces led to the deaths of 135 people.
Government spokesperson Damantang Camara later said that a deal to end the strike was signed with Guinea's main teachers' unions.
The unions had launched the strike on Feb. 1 to protest the government's decision to dismiss or cut the salaries of many junior teachers after the latest civil service exams, and many of their students had taken to the streets in recent days to support them.