It's the toughest challenge in rugby, possibly the toughest challenge in sport.

The All Blacks at a World Cup.

New Zealand have won the last two World Cups and have not lost a match in the tournament since 2007.

South Africa, one of the pre-tournament favourites, were swatted aside. Canada were thrashed.

Namibia, the lowest-ranked team in the tournament, are next to give it their best shot - a team that includes a number of amateurs.

Here's the monumental task facing the Welwitschias on Sunday.

Namibia's monumental task

New Zealand's recent dominance at Rugby World Cups has been as commanding as anything seen in sport.

They have won a record 16 matches in a row the competition, a run that goes back to a quarter-final defeat to France in 2007 and has seen them lift the Webb Ellis trophy in 2011 and 2015.

The All Blacks have incredibly never lost a group stage match at a World Cup. Their current record is played 30, won 30.

At World Cups they have played 16 matches against non-tier one teams and have not lost any.

Against tier two teams and below the All Blacks average a winning margin of 59 points at World Cups, scoring an average of 10 tries per game.

The 63 unanswered points that the All Blacks piled up against Canada in Oita was the biggest margin of victory any team has managed at the 2019 World Cup so far.

In comparison, Namibia have not won any of their 21 matches at World Cups - the most matches of any side yet to win.

Namibia's worst-ever World Cup defeat was in 2003 when Australia ran up a cricket score to win 142-0 at the Adelaide Oval.

The last time Namibia beat a tier one nation was when they defeated Ireland 26-15 in Windhoek 28 years ago.

Some bookmakers have the African side at odds as big as 250-1 to win.

'We have nerves and excitement'

Namibia and New Zealand met at the 2015 World Cup with the All Blacks winning 58-14 in London.

Centre Johan Deysel said scoring Namibia's try in that game was the "best moment" of his career and admitted he feels both nerves and excitement about playing the All Blacks again.

"You are playing the best team in the world and have to rock up and face the Haka and have a big crowd around you," Deysel, now Namibia captain, said.

"What an opportunity it is for us - coming from a small country to play the best in the world.

"You always dream about it as a young boy. You see it on TV and can just imagine standing in front of them."

But will that dream become a nightmare on Sunday?