A police spokesman described the scene as a "graphic homicide".
The bodies were found by firefighters after neighbours in the building reported a suspected gas leak.
The building was initially evacuated and roads in the area closed for fear of an explosion but police later said they believed there was no gas leak.
"We're looking at perhaps a very dramatic homicide scene with as many as six dead," said Sgt Roger Morrow of the Royal Canadian Mounted Police (RCMP).
He said he did not know if it was a murder-suicide.
Identity unknown
Residents of the large block of flats in Surrey, outside Vancouver, may have mistaken the smell of decomposing bodies for a gas leak, said RCMP homicide investigator Cpl Dale Carr.
"We have not yet been able to determine who these individuals are," said Cpl Carr.
"We have not been able at this time to determine the gender or the race of these individuals," he added.
The bodies were discovered Friday afternoon by firefighters who were called to investigate a suspected gas leak.
Map highlighting Surrey B.C.
At least six people are confirmed murdered inside a high rise apartment located in Surrey just outside of Vancouver, British Columbia in Canada, in what is being called a "graphic mass-murder". The bodies were discovered on October 19 at approximately 4:30 p.m. (PT).

Residents living near the house called authorities when they reported the smell of what they believed to be natural gas, coming from inside the house and that there were possibly several people inside. The fire department and police arrived in full force and told nearby residents to evacuate, shutting down the roads and stopping train service surrounding the property. When police later entered the home, they discovered the six individuals. The murder is still under investigation, along with the reports of a gas-like smell.

"We're looking at perhaps a very dramatic homicide scene with as many as six dead. Initially, it was a report of a gas leak. A very large area was cordoned off for fear of an explosion. As to how this call comes in as a gas leak, that's going to come out in the investigation", said Royal Canadian Mounted Police spokesman, Sgt. Roger Morrow.

The identity, race and sex of the individuals are not known. Police also have not yet determined if the mass murder was a result of a murder-suicide. Police have not stated the form of murder and there are no reports of any suspects being in custody.

"It's hard to say whether its gang-related, some sort of attack on a group of individuals, or whether it's a murder-suicide. Certainly it's a concern to us and we understand it's a concern in the community", said Integrated Homicide Investigation Team member, Cpl. Dale Carr.