At least 150 people were wounded in the latest violence in the West African country, the BBC reported.
The union and opposition-party protesters in the capital of Conakry, want President Lansana Conte to resign, alleging the diabetic in his 70s is too sick to govern.
More than 30,000 demonstrators marched to the parliament building chanting "Enough" and "Bye-Bye Conte."
Anti-protester killings were also reported in other towns, the BBC said.
U.N. Secretary-General Ban Ki-moon and African Union Chairman Alpha Oumar Konare have called for dialogue between the two sides in the two-week strike.
Food prices have risen sharply in Conakry, with staple foods including rice and bread in short supply, the report said.
Transparency International, a leading international non-governmental organization addressing corruption, said in November that Guinea under Conte was the second most corrupt country in the world after Haiti.