"There's no magic bullet in these by-elections - you've just got to work your butt off," Mr Anderton said.
Mr Anderton, the former Labour MP-turned-Alliance leader and Progressive Party leader, said he only accepted an invitation from former leader David Shearer to run the by-election because he knew it was going to be hard.
It was not easy because the electorate was hardest hit by the earthquakes.
"There have been huge closures and God knows how many houses have gone. There are whole streets in the electorate that are empty; it's a bit like Beirut on a bad night and the roads are virtually third world."
The seat was vacated by Lianne Dalziel who is now the mayor of Christchurch.
Ms Williams moved to Christchurch after the 2011 election, although she had family living there. She is a manager of a community service provider. National candidate Matthew Doocey is a healthcare manager and returned to Christchurch only this year after working in Britain.
The fact that Poto Williams was not in Christchurch during the earthquakes was not important, Mr Anderton said.
So has he rejoined the Labour Party? "I have not. Never am I going to do that. I left the Labour Party and I do not intend to return."
But if he had a choice between Labour and National, he would back Labour.
Prime Minister John Key will be campaigning in Christchurch today and Labour leader David Cunliffe will arrive tomorrow.
Act leader John Banks was likely to be campaigning in Christchurch East today.
The candidates
• Leighton Baker - Conservative
• Matthew Doocey - National Party
• Ian Gaskin - Independent
• Adam Holland - Independent
• Paula Lambert - Aotearoa Legalise Cannabis Party
• Jenner Lichtwark - Democrats for Social Credit
• David Moorhouse - Green Party
• Sam Park - Independent
• Gareth Veale - Act Party
• Poto Williams - Labour Party