The attack, which took place at the city's Quebec Islamic Cultural Center, is being investigated as an act of terrorism by police.
In what was described as a coordinated attack, witnesses say at least two gunmen wearing black fired indiscriminately into the dozens of worshipers -- including families -- in the mosque.
Thirty-nine people who were at the mosque during shooting were unharmed, Christine Coulombe, spokeswoman of National Police of Quebec, said. Of the eight injured, six are described as being in critical condition.
Two people have been arrested, a police press conference confirmed.
Edited From Cnn