A woman is dead and three people, including two children, are in hospital after a stabbing in East Gwillimbury Saturday afternoon. A 37-year-old man, believed to be the suspect, was fatally shot by police, the province's police watchdog said.

Emergency crews were called to a home in the area of Vivian Creek Road and Ridge Gate Crescent in Mount Albert just before 2:30 p.m. for reports of a stabbing.

When officers arrived, they found a woman deceased at the front door of the home. York Regional Police Const. Laura Nicolle said officers also located an infant, a young child and another woman with serious injuries.

They were transported to hospital. Police have not released the names or ages of the victims.

Nicolle said the suspect was killed following an altercation with officers.

In a news release issued Saturday evening, the Special Investigations Unit said police entered the home and became involved in an interaction with a man. Two officers discharged their firearms, striking the man, the SIU said.

He was pronounced dead on the scene.

Five investigators and four forensic investigators have been assigned to the case, the SIU said. Two subject officers and one witness officer have been designated.

The SIU investigates incidents involving police officers where there has been death, serious injury or allegations of sexual assault.

Nicolle said there is no outstanding suspect.

"I don't have any information just yet as far as what the relationship would have been or the connection," she said. "There's nothing that suggests that this would have been random, so obviously, that's going to be something we're looking at."

While there is no threat in the community, Nicolle said residents should expect a large police presence in the area as they investigate the incident.

"We know this is a very quiet street and neighbourhood, and people are going to be worried when they see this type of presence. But we do want to reassure people that we're here, we're investigating, and there isn't anything that they need to be concerned about," she said.

"But certainly, if they have information, please come forward."

East Gwillimbury Mayor Virginia Hackson issued a statement following the incident.

"This is a most tragic situation and I am deeply shocked and saddened to have this happen in our small community of Mount Albert," the mayor said.

"On behalf of Council, I extend our heartfelt thoughts and prayers for the victims, their families and friends."

In a Twitter post, York-Simcoe MPP Caroline Mulroney said her heart breaks for the victims of the tragedy.

"My thoughts are with the victims and the first responders," Mulroney said. "Mount Albert is a strong community and will come together to support each other through the days ahead."