The gas contractor who'd worked at the Christchurch home that suffered a massive gas explosion last week, hospitalising six people, has offered his condolences to the families.

The local gas company owner-operator was "distraught" by last Friday's events, his lawyer Simon Shamy told the Herald today.

He'd looked at the Northwood property's gas issues just one day before it exploded, it's understood.

While his client is legally unable to speak to media at this stage, Shamy says he has reached out to the families injured in the blast and offered his sincerest condolences.

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Shamy also stressed that he would co-operate with any investigations, and noted that the gasfitter fronted to police at the scene on the day of the explosion. He couldn't comment further, the lawyer said, while both the police and WorkSafe inquiries are ongoing.

Neighbours and passers-by who pulled stunned survivors from the burning debris were amazed that nobody was killed instantly in last Friday morning's blast.

Two patients today remained in Christchurch Hospital, with one in a stable condition and another in a serious but stable condition.

A third person remains stable at Auckland's Middlemore Hospital, which has a serious burns unit.

Three others have since been discharged from hospital over the last week.

The daughter of the worst injured survivor says the family are still too upset to talk to media.

The 10.14am explosion obliterated a Marble Court house in the northern suburb of Northwood. Blast waves scattered chunks of roof tiles and other debris around the neighbourhood.

Several neighbouring houses have major damage, including blasted walls, caved-in garage doors, smashed windows and eaves.

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Christchurch City Council has issued four Dangerous Building notices, which prevent "use or occupation" of the properties. Another five houses have been issued Restricted Access notices, which only allows specific people like insurance agents, structural engineers, specialists, builders or tradespeople, and owners "for retrieval of personal items" in the building.

Canterbury Metro Area Commander Superintendent Lane Todd earlier this week said WorkSafe is now acting as lead agency, working with police and Fire and Emergency New Zealand.

During its probe, WorkSafe says it will work to determine "the immediate and underlying causes" of the event.

As well as the Health and Safety at Work Act 2015, WorkSafe is the regulator for ensuring the safe supply and use of electricity and gas in New Zealand under the Gas Act 1992 and the Electricity Act 1992. Its mandate with energy safety includes workplaces and homes.

WorkSafe investigations can take up to a year to complete.

Some homeowners face a long wait before they can return to their properties, with a cordon around the worst-affected houses.

Indraj and Akita Fonsaka who live across the road said on the weekend that friends and family were looking after them as they said their insurance refused to stump up for temporary accommodation.

Their lives have been thrown into turmoil and, like many of their neighbours, they are unsure when, if ever, they'll be allowed home.

"We were living very peacefully here," said Akita.

"We have lovely neighbours, it's just a nice quiet street."