A dramatic hostage situation at a bank north of Toronto ended abruptly on Wednesday when police killed a lone gunman.

No one else was injured but those inside the Royal Bank of Canada branch in Maple, Ont., were "definitely traumatized," said York region police Const. Andy Pattenden.

"We did have to use lethal force in order to gain control of that subject," Pattenden said.

Police raced to the scene after a call at about 1 p.m. and arrived at the branch to find a gunman as well as a number of other people inside, both staff and clients.

"Officers arriving on the scene were able to get some of those inside out to safety," Pattenden said. "It did turn into a hostage situation for us."

The bank is located in a plaza along with a child-care centre, dentist office, drug store and other outlets. Police said many people were in the plaza at the time, and some reported being told to take cover as the drama unfolded. A negotiating team was brought in, to no avail.

Daycare owner Ellana Katzberg told CTV News that she sent an alert out to parents on her phone when police evacuated the plaza

Officers helped staff carry dozens of children between the ages of 10 months and four years old to the safety of a nearby transit bus.

"We were able to send out an emergency alert to parents right away," Katzberg told CTV. "Everybody knew where we were and we were in touch with parents throughout the time."

Investigators were still in the process of clearing the bank and checking a vehicle to try to find out more about the man and his motivation.

Pattenden said he had no details on how many people were caught up in the bank or whether the man made any specific demands.

"I can't even tell you it was a robbery," Pattenden said. "(But) being in the bank with a gun was very threatening."

The plaza with the bank was cordoned off with police tape by Wednesday evening and many officers remained at the scene. At least a half dozen people who were in the bank at the time of the incident were taken to an ambulance bus nearby, many with white blankets wrapped around their shoulders.

In a statement, RBC said it was "extremely relieved" customers and employees were safe.

"Out of respect for our clients and employees who were involved in this incident, and the ongoing investigation, we will not be commenting further," the bank said.

Ontario's police watchdog, the Special Investigations Unit, is reviewing how officers handled the incident.

SIU spokesman Jason Gennaro told reporters on Wednesday evening that two police officers used their firearms during the interaction with the gunman.

He said he could not identify those involved, but said the 25-year-old gunman was pronounced dead on scene.

"The SIU's investigation is going to be focused on the interaction between the police officers and the individual," Gennaro said. "Of course as a part of that investigation, we're going to look at to determine what happened in the lead-up to that event."

Gennaro said the SIU, which investigates all deaths where police are involved, has brought in eight investigators and four forensic investigators.

— with files from Colin Perkel in Toronto.

Keep reading