OTTAWA -- Canada's chief electoral officer has laid out the scale of the challenge for Parliament if it wants to change Canada's voting system in time for the next federal election in 2019.

Elections Canada will need a full two years to prepare should the Liberal government make good on its promise to end the current first-past-the-post voting system, Marc Mayrand told a special parliamentary committee Thursday studying electoral reform.

If new legislation is enacted by May 2017, Mayrand said that would provide enough time to prepare for the next fixed election.

"It should be OK, but you should not underestimate the challenges that it will represent."

He raised a host of technical and timing issues that will need to be addressed, including changes to his educational mandate under the Fair Elections Act, changes to the law governing federal riding redistribution, and potentially changes to the Referendum Act.

There are some 40 information technology systems at Elections Canada that would have to "tuned" or completely overhauled, he said, and training thousands of temporary election workers on a new voting system would be a major undertaking.

Mayrand noted it took 26 months of public consultations to hash out the creation of 30 new ridings before the 2015 election, even without altering the fundamental way MPs are elected.

"If the (new) changes are complex, the campaign will have to start earlier and be even more ambitious," he told the all-party committee.

Mayrand also said that if the committee decides a referendum is necessary to endorse a voting change, it would take six months to organize and cost about $300 million -- a time frame that further complicates the May 2017 deadline for a decision.

"Our estimate is that, under the current Referendum Act, it would be around $300-million to run a referendum," he said.

Mayrand was just the second witness to appear at the extraordinary summer committee hearings, following an appearance by Democratic Institutions Minister Maryam Monsef on Wednesday.

The chief electoral officer announced earlier this year he'll step down at the end of 2016, so the task of electoral reform will fall to his successor.

But Mayrand said Elections Canada has already begun "contingency plans" for a potential electoral reform referendum, something the Conservative official Opposition has been loudly demanding since the Liberals took office on a pledge to make 2015 the last federal election under the current voting system.

He noted it took New Zealand almost 10 years to change its electoral system, from the time of the first committee hearings to the election that deployed the changes.

He also told the committee that extensive public education over a long period will be crucial if the voting system is changed, and that Elections Canada's mandate will need to be expanded to allow it to perform this function. The former Conservative government restricted Elections Canada's educational mandate under the controversial Fair Elections Act of 2014.

The departing electoral officer concluded his two-hour appearance with a sobering caution to the MPs.

Mayrand said multiple surveys have shown "Canadians have extremely high level of trust in their elections system and this is very fragile. Once you lose it, its very difficult to regain.

"So my caution, or my point here, is be extremely careful and sensitive to anything that's being done that may impact the trust of Canadians."