OTTAWA -- A request for a two-year extension from the national inquiry into missing and murdered Indigenous women and girls is getting a mixed response from First Nations leaders.

Commissioners formally asked the government Tuesday for more time and another $50 million to allow it to finish its work by December 2020.

The Native Women's Association of Canada said it supports the revised timetable, saying more time is necessary for the commission to fulfil its mandate of uncovering the root causes of violence against Indigenous women and girls.

The group's president, Francyne Joe, said the extension will allow the inquiry to hear from survivors and family members who still want to share their stories.

"The inquiry has a great deal of work to do on behalf of Indigenous women and girls," Joe said in a statement.

"Without more time to complete a full array of expert and institutional hearings, the inquiry risks simply replicating existing research."

The association comprises 13 native women's groups from across Canada.

But Grand Chief Sheila North of Manitoba Keewatinowi Okimakanak, a group that represents 30 First Nations in the province's north, said on social media she can't support the extension without changes to the commission's leadership.

"It's not too late to make process more meaningful for .MMIW families/survivors," she posted on Twitter.

North was one of several high-profile chiefs across the country who called for the inquiry's head commissioner Marion Buller to resign in order to reset a process they described as falling apart.

In December, a special gathering of chiefs hosted by the Assembly of First Nations voted to ask the federal government to replace Buller.

The assembly supports extending the inquiry's timeline and that anything less would suggest the safety and security of First Nations is no longer a priority, said Chief Denise Stonefish, chair of the organization's women's council.

"If the federal government wants to truly stand with survivors and their families and support the journey toward healing and reconciliation, then it has to extend the national inquiry, while accommodating any changes required to ensure the prevention of violence and the support of all families at risk," she said in an email.

Indigenous Relations Minister Carolyn Bennett confirmed Tuesday she received the commissioners' request and would consider a response after consulting Indigenous partners and her provincial and territorial counterparts.

Buller said Tuesday more time and money is needed to hear from the hundreds of people still waiting to share their stories and the commission's work is a "sacred responsibility."

The inquiry began its work in September 2016 and an extension would nearly double its original $54-million budget and push back the due date for its final report to December 2020.

So far, more than 760 witnesses have testified at nearly 250 hearings across the country and about 630 more have registered to participate.