A meteorite is believed to have burned up over Canterbury today before slamming into the ground in a field.

A loud boom heard throughout the region was most likely to be from a meteorite, up to the size of a medicine ball, Stardome Observatory in Auckland says.

The loud boom was heard over Canterbury, with sightings as far afield as Hanmer Springs in North Canterbury, and Hinds in Mid-Canterbury.

Observatory spokesman Andrew Buckingham told NZPA: "We're still finding out what's going on".

Initial reports had come through the police communications system, with follow ups from eyewitness accounts.

"It sounds like a large meteor coming down... soccer ball size upwards," Mr Buckingham said.

It was more likely to be one large rock entering the earth's atmosphere as a fireball, rather than a meteor shower.

The boom was either the meteor breaking the sound barrier or exploding as it burned up.

Stardome Observatory in Auckland's spokesman Andrew Buckingham said it was not a particularly unusual event.

New Zealand had one or two fireballs a year.

This one had been "at a time and place where people have seen it".

It sounded very similar to a bright fireball seen in Taranaki on July 7, 1999, he said.

Stardome wanted to see camera or film footage of the fireball, he said.

Emergency services were inundated with calls from the public about the noise, with initial reports suggesting a meteor strike.

A Christchurch Fire Communications spokesman said the first calls from the public started at 2.53pm today, with people reporting windows rattling and the air "shaking".

There was speculation a "sonic boom" had been caused by space debris, he said.

Several people reported seeing a glowing red ball streaking over the Canterbury sky.

"Whilst sunning myself in Ilam, I saw a bright meteorite fly high over one of the buildings with a yellow tinge. It continued for about five seconds before breaking off into two smaller pieces and disapearing. Seconds later a loud rumble permeated the air, which startled me," said Georgia Weaver from the University of Canterbury.

The meteor has shown up on the McQueen's Valley seismograph.

A GNS Science spokeswoman said they were aware of the incident.

"Something has hit the ground hard, it's not an earthquake," she said.

An Air Force spokesman told NZPA none of their aircraft were responsible - none of the current fleet went fast enough to create a sonic boom.

The Christchurch airport had reported they had no planes that were capable of making such a noise.

Kevin Graham, garage workshop owner in Rolleston - 22km southwest of Christchurch - told NZPA when he heard the boom his first thought was it was a September 11 anniversary attack.

"I don't frighten very easily, but I was just about sh**ing myself."

Mr Graham said he was inside his workshop at the time the boom hit.

"I've been talking to my wife at Addington and she had run outside because she thought the stand was going to collapse. And I ran outside because I thought my place was going to collapse as well."

Mr Graham said he could feel the shock waves in the air so thought it was close, but a truck driver had reported to a local rep he had seen a meteorite fall from the sky into a field in Hinds, 19km southwest of Ashburton.

He said the sound was like a CNG tank exploding.

"It started off with a little boom then a real massive boom. And I mean massive - like the daddy of all booms."

The noise was so loud it shook the garage, he said. "I was wondering what happened and I thought 'Oh, September 12', because we're a day ahead of the States.

"As you do, because everyone is talking about it at the moment."

Hanmer Springs police officer Senior Constable Chris Hughey likened a meteor shooting across the skies over Canterbury today to Haley's Comet which he saw when it last passed near Earth in 1986.

Mr Hughey said he saw the meteor to the south of the North Canterbury resort town just before 3pm and it appeared to be coming in on a 30deg angle travelling west to east.

"All it looked like was a vapour trail from a plane coming in at huge altitude," he said.

"It was a crystal clear day here in Hanmer and it appeared to have a red ball or something at the front. Then it split into about three and just disappeared."

Mr Hughey said he did not hear the loud sonic boom that was heard in Christchurch and elsewhere.

"We didn't have the explosion. It wasn't that overly startling from here, but it was something I've never seen before."

Mr Hughey said he'd seen a few small meteors "coming in here and there" over the years but nothing like today's one. . ."never coming in on that angle.

"I've seen them going horizontally across the sky.

"I've never seen one coming virtually straight down like that.

"It just disintegrated at great altitude. It was moving, too. I don't know what speed they come in at, but it was going."

Mr Hughey said the show lasted no more than a few seconds.

"I called a radio station and told them to expect a few calls," he said. "I don't think they believed me."