TORONTO -- An appearance by Prime Minister Justin Trudeau at an event for Liberal supporters in Toronto was interrupted by a protester from Grassy Narrows First Nation Thursday.

The unidentified woman called on the federal government to make good on its promise to provide a mercury treatment centre for the northwestern Ontario community.

She cut into a question-and-answer session with Liberal MP Adam Vaughan to hand Trudeau a letter, stressing that people continue to suffer from mercury poisoning in the area.

"It has been 500 days since you have promised the community, your government has promised the community," she said.

"People continue to be sick and die from mercury poisoning. And I know that you care. You're a caring person. So this is why I give the letter ... I hope you get it."

Trudeau thanked the woman and told her she was welcome to stay.

"You are among friends here but I understand how difficult the situation is for you. For people in Grassy Narrows," he said.

Trudeau said his government is working with the provincial government to solve the problem, and that his minister of Indigenous Services has met with the chief in Grassy Narrows.

"We are working towards solving this challenge, but I agree. We are all impatient to move forward in a way that gives healing to that community and the kind of support and future for everyone in that community and across Indigenous communities in this country."

This is the second Liberal event in recent months that has been interrupted by a Grassy Narrows protester.

In March, Trudeau apologized for his response to a protester who interrupted a Liberal fundraising event to draw attention to the mercury poisoning in Grassy Narrows.

As security escorted the woman out, Trudeau thanked her for her donation: "I really appreciate your donation to the Liberal Party of Canada."

People in Grassy Narrows have had health problems for decades linked to chemical-waste mercury dumped into the English-Wabigoon river system throughout the 1960s and 1970s.