CHRISTCHURCH, New Zealand – New Zealand was warned on Tuesday to brace for more than 240 deaths from the Christchurch earthquake, as the country prepared to observe two minutes' silence for the victims.

The official toll stands at 154 after last week's devastating 6.3-magnitude quake in New Zealand's second largest city but police said it was likely to rise to 240, up from a previous estimate of more than 200.

"We need to start considering the figure of around 240 but (it's) not locked in stone, because we're still getting information in," district commander Dave Cliff told reporters.

As the estimate of fatalities rose, Prime Minister John Key promised a major inquiry, saying there were legitimate questions about why so many office blocks collapsed in supposedly "quake-proof" Christchurch.

"There has to be an inquiry," Key told Radio New Zealand, as rescuers continued to comb the city's ruins for bodies.

"We have to provide answers to people about why so many people lost their lives and we have to learn lessons from the earthquake."

Key said the quake may simply have been a violent act of nature but the country owed it to the dead to find out if the destruction could have been prevented.

"Some things may have been just beyond our control, it's an act of nature and it's had a devastating effect, but we owe it to those people to give them answers about what went wrong," he said.

Officials warned the catastrophe would also hit the country's struggling economy, wiping out any growth in the financial year to June.

"June-to-June could be close to zero growth," Finance Minister Bill English told public radio.

"It's a different outlook from what we expected six months ago but we'll just have to roll with the punches."

John Key has asked all New Zealanders to fall silent at 12:51pm (2351 GMT Monday), exactly one week after seismic jolt tore the city apart.

Mayor Bob Parker said the tribute would be an emotional moment.

"Whatever you are doing, stop... and we'll all stand together as one," he told TVNZ.

Exhausted emergency crews with sniffer dogs and sensitive listening devices are scouring the wreckage but admit hopes of finding more survivors have evaporated.

"It is probably highly unlikely that we will encounter live victims within collapsed structures," the fire service's rescue operation manager Jim Stuart-Black told reporters.

No survivors have been found since a woman was pulled from a collapsed office building on Wednesday afternoon, a day after the quake hit. Rescuers had said earlier they hoped for a miracle.

The broken city has begun the grim task of burying its dead, with hundreds of weeping mourners gathering Monday for the first funeral of a quake victim, a five-month-old baby boy called Baxtor Gowland.

"Bax you are forever in our hearts we will always love you xo," his father Shaun McKenna wrote on a Facebook tribute page to the infant, who was born just after a 7.0 quake last September, that miraculously claimed no lives.

The scarred city is also facing the hazard of violent aftershocks, with one measuring 4.3 hitting on Tuesday, creating treacherous conditions for emergency crews from around the world who have flown into the city to help relief efforts.

The shakes have opened cracks in a cliff overlooking suburban streets and threaten to cause landslips, forcing residents to flee their homes and further jarring the stretched nerves of locals.

In one small piece of good news, a windstorm forecast to pack gusts of up to 130 kilometres (80 miles) per hour failed to materialise Monday but forecasters said gale force winds could still whip through the city on Tuesday night.