Aucklanders considering house additions or alterations could be out of luck as builders prepare to converge on Christchurch.

Keith Roberts from the trade website Builderscrack has posted a special web link to match tradespeople with homeowners and is already seeing many northern specialists put themselves in the market for the $4 billion rebuilding of Canterbury.

He said that although it was early days and much of the work would not start until insurers had approved claims, a number of the 3600 tradespeople registered with the business had just listed Christchurch as an area where they would work.

Blair Cranston of Cranston Homes in Silverdale said he had also heard of a number of builders considering heading south.

Subcontractors from Napier, Queenstown and Dunedin are also preparing for the rebuild.

Jeremy Wyn-Harris of Builderscrack in Christchurch said he had heard of a lot of interest from northern builders and subcontractors "but I don't think there are many on the ground yet. As the insurance claims start to clear, there will be a huge pickup in demand ... It doesn't make sense for people to arrive without work secured."

However, a recruiting expert is warning that Christchurch is no goldmine. Kevin Eder, managing director of Tradestaff in Christchurch, said some construction workers expected to get double their usual rates, peaking around $50-$55 an hour. That could result in greedy subcontractors scamming Cantabrians for $2000 a week.

"But we think that's just misguided," he said. The rebuilding would not be quick and it was wrong to view the city as a goldmine with an immediate rush of work.

"These people might be earning $20-$25 an hour so they think, 'We will go to Christchurch and get $45-$55 an hour."'

Canterbury homeowners are being warned by the police and building experts to beware of cowboys.

Registered Master Builders told Canterbury property owners to take care whom they chose for rebuilding work after complaints about fly-by-night chimney repairers.

Inspector Dave Gaskin said Christchurch residents, including an elderly woman, had contacted police after people claiming to be tradesmen had offered to remove damaged chimneys and do other repair work.

Builderscrack had 886 jobs nationally available this week and it highlighted earthquake jobs which included:

A broken water pipe at North Linwood where one tradesperson was talking to the homeowner.

A collapsed chimney in Woolston where eight builders wanted to quote.

Problems at an Avonhead house which called for builders, piling/foundation specialists, bricklayers, surveyors and engineers to fix a cracked chimney, cracked kitchen walls, cracks in an exterior brick wall and fine cracks in the exterior.

Graeme Earl, Canterbury Registered Master Builders Association past-president, said some tradesmen were already overcharging, ramping up their hourly rates and some were adding a premium for quake jobs.

"Hopefully, that won't last, and they will be knocked out of the market."