CALGARY -- Police say a stabbing at a Calgary medical clinic in which a man was killed appears to be domestic in nature but they aren't saying what may have led to the attack.

Officers who arrived at the Perpetual Wellness Chinese Medicine Centre on Thursday afternoon also found two other people with non-life-threatening injuries.

One woman was transported to hospital and a second person was treated on scene before being taken into custody.

Police didn't give any further details about the suspect, who was arrested at the clinic without incident and has not yet been charged.

"I can't speculate on what the thought process of the suspect was going into this, but I can tell you that all three people were known to each other and it's domestic in nature," said duty inspector Dean LaGrange.

Police believe the attacker and the woman were romantically involved, or had been in the past, he said.

LaGrange did not say how deceased, the proprietor of the clinic, was related to the suspect and the woman.

The three involved were in their 40s and 50s, he said. Six witnesses were being interviewed by homicide detectives.

There were large drops of blood leading up to the door of the clinic. Yellow police tape blocked off the section of mall while bystanders looked on. A single policeman stood in front of the business.

Maggie Law runs a spa a few doors down from the wellness centre.

"Someone was at my door and something happened. I just saw the restaurant people running over to help and were yelling, 'Bring more towels, bring more towels! There's a lot of blood,"' she said.

"Then I went back to look at what was happening and saw two guys on the floor. I think it was two guys, I only saw their legs. It was really messy and there were some towels and then the police came."

Law said about 15 minutes later, she saw one man being brought out in handcuffs.

She said she didn't hear anything when the attack happened and the mall for the most part is usually quiet.

Several lanes of a major Calgary street were blocked off at one point as officers investigated what happened at the Central Landmark Building.

The area is north of downtown Calgary.

A salesman with an optician business in the building said no one was allowed to leave for a couple of hours.

"By the time it all started, the cops actually cordoned off everything, so it was basically on lockdown. We couldn't leave," said Nick Wong with Essential Eyewear.

"Between two and 4ish, there was basically yellow tape everywhere. Upstairs was basically off limits."