The five, including three women, suffered serious injuries and were rushed to hospital, officials said.
The police blocked roads and fired several rounds of tear-gas canisters to disperse the protesters when many were hit by the shells.
The Manipur unit of the Bharatiya Janata Party has been agitating against the cancellation of the selecion tests of 2013 for recruiting 2,000 constables.
State BJP President Khetrimayum Bhabananda said, "The police crackdown on the unarmed people holding democratic protest only shows the mentality of Chief Minister Okram Ibobi Singh."
Senior leader Nimaichand Luwang said, "No candidate of the 2013 recruitment tests had participated in the fresh tests held on August 30."
Levelling serious allegation, Luwang said: " Those candidates who were tipped to be selected were cherry-picked, brought to Imphal in police vans and kept in the two Manipur Rifles camps for stage managing the recruitment tests."
He said the BJP has the support of the entire people of Manipur as "this is corruption".
BJP legislagtor Khumukcham Joykishan said: "The fresh tests were illegal as they were against the Supreme Court ruling, which says there should be a gap of 15 days between the tests for job interviews for all vacancies, whereas there was only a 10-day gap in this case."
BJP state spokesperson N. Mangi told IANS: "There will be democratic form of protests on Monday, the last day of the two-day sitting of the monsoon session of the assembly."
Meanwhile, the state government said that recruitment tests were being conducted in all districts peacefully.
