Police are urging people to "stay in their homes with doors locked at this time for their safety" as the incident continues.
The Fredericton Police Twitter account says: "An incident has resulted in at least four people killed."
The incident in the capital of the Canadian province New Brunswick is still ongoing.
Police are urging people to "stay in their homes with doors locked at this time for their safety" and to avoid the area of Brookside Drive between Main and Ring Road.
A New Brunswick journalist has reported that four shots were heard at around 8.20am local time (12.20pm GMT).
She also reported that people were being escorted out of the area by police.
Chris Collins, Speaker of the New Brunswick Legislative Assembly, tweeted: "In light of the horrible news coming out of Fredericton, I have ordered all flags to half mast on Legislative grounds."
Numerous emergency service vehicles can be seen on the residential road.
The Fredericton Firefighters Association warned social media users not to report on police locations during the on-going incident, writing: "Police, Fire and ANB responding to an active incident. Please avoid the area of Brookside Dr between Ring and Main. Stay in your house and businesses. Lock the doors and do not use social media to report on police locations. Please help keep everyone safe."
The City of Frederiction Twitter account announced that public transport was being re-routed to avoid the Brookside Drive "until further notice".
Police said the station as been inundated with calls and asked the public to "refrain from calling the police station directly" and to call 911 if there is an emergency.