The presidential nominee hopeful made the remark on Sunday during an interview with NBC television.

He said concerned constituents raised the issue of security during meetings in the US state of New Hampshire, which shares a border with the Canadian province of Quebec.

Walker confirmed he would be open to constructing a border fence to secure the northern border, similar to the wall with Mexico.

"Some people have asked us about that in New Hampshire. They raised some very legitimate concerns, including some law enforcement folks that brought that up to me at one of our town hall meetings about a week-and-a-half ago," Walker told NBC.

"So that is a legitimate issue for us to look at."

Canada and the US share the world's longest border, most of which is undefended.

At 8,891 kilometers (5,525 miles) long, the Canada-US boundary is the world's longest international border.

Elections race heats up

Immigration is a hot-button issue in the race to the November 2016 elections. Donald Trump, who is the leading contender for the Republican nomination, has further incited debate by promising to force Mexico to foot the bill for a wall between the US and its southern neighbor. His comments angered many Hispanics, an important segment of the American voting population.

The real estate tycoon also said he would end automatic citizenship for those born in the US, a right enshrined in the 14th amendment to the US Constitution. The measure was initially added to ensure citizenship for the descendants of slaves.

Trump is leading the 17-way Republican race with 28 percent of voters supporting the billionaire nationwide according to a survey released on Thursday. That is a jump of 8 percent from a similar survey in July by Quinnipiac University.

Walker is currently ranked sixth with six percent. This is a slip from a few months ago when he led the polls in the Iowa caucuses in February

kb/jil (AP, AFP)