CHRISTCHURCH, New Zealand — A sharp series of about 20 aftershocks rattled New Zealand's earthquake-hit city of Christchurch overnight, and earthquake experts warned Tuesday that another powerful temblor might hammer the region in coming days.

The weekend's powerful 7.1-magnitude earthquake smashed buildings and homes, wrecked roads and disrupted the central city, though nobody was killed and only two people were seriously injured — which authorities attributed to good building codes and the quake's early-morning timing.

"It was as strong as the earthquake in Haiti earlier this year, which caused widespread devastation and is estimated to have killed approximately 230,000 people," Prime Minister John Key said Tuesday. "Although no one lost their life ... families have been traumatized and lost their valued possessions."

The city center remained cordoned off by troops Tuesday, with only building owners and workers allowed in to begin clearing up the mess — with much of the center taking on the mantle of a ghost town.

More than 100 aftershocks, ranging from magnitude 3.2 to 5.4, have rocked the region since Saturday's major quake.

Overnight, about 20 shocks including two of magnitude 5.4 rattled the city, and quake experts said aftershocks likely will continue for several weeks — and the worst of them may be yet to come.

"It is still possible that we'll have a magnitude-6 in the next week, and people ought to be aware of that, particularly if they are around structures which are already damaged," said Ken Gledhill, a monitor at the geological agency GNS Science. "For a shallow earthquake like this, they will go on for weeks."

Key called off a planned nine-day trip to Britain and France, citing what he called the quake zone's continuing "instability."

Key was to have met with British Prime Minister David Cameron and French President Nicolas Sarkozy, and with his wife, Bronagh, to have spent a weekend with Britain's Queen Elizabeth II at her Scottish castle, Balmoral.

The New Zealand government has said it plans to pay at least 90 percent of the hundreds of millions of dollars needed to rebuild Christchurch's water, waste water and road infrastructure.

In a statement Tuesday to Parliament, Key pledged to remove bottlenecks to reconstruction and said the government "is prepared to step up financially to rebuild the region."

He planned to return to the damaged city later Tuesday to meet victims displaced by the quake and for talks with local officials.

"As the frightening aftershocks continue, we stand alongside them (people of the region), committed to helping them rebuild their lives," he said.

The main quake struck at 4:35 a.m. Saturday near the South Island city of 400,000 people, ripping open a new fault line in the earth's surface, destroying hundreds of buildings and cutting power, which has been gradually restored in recent days.

The government has said that at least 100,000 of the region's 160,000 homes sustained some damage.

New Zealand sits above an area where two tectonic plates collide. The country records more than 14,000 earthquakes a year — but only about 150 are felt by residents. Fewer than 10 a year do any damage.

New Zealand's last major earthquake registered magnitude 7.8 and hit South Island's Fiordland region on July 16, 2009, moving the southern tip of the country 12 inches (30 centimeters) closer to Australia.

Associated Press Writer Ray Lilley in Wellington contributed to this report.