Passengers and airport staff hurt when 200 ceiling tiles fell at Auckland International Airport yesterday have all been released from hospital.

However, 22 check-in counters at the airport remained closed today as airport staff, Occupational Safety and Health inspectors and builders tried to find out what caused the tiles to fall five metres on to passengers and check-in staff.

Most of the 15 hurt were airline staff and five were taken to hospital. The rest were treated at a Mangere medical centre.

The area was opened on Tuesday and included 12 new counters and 10 old counters.

Auckland International Airport general manager (corporate) Chris Curley said eight of the old counters may be reopened today . However the rest would stay closed until the investigation found out why the tiles fell and the company was sure it was safe.

It was too soon even for an initial finding on the collapse, Mr Curley said.

"It opened on Tuesday and had a code of compliance from the city council. All the tests had been done. It had been checked and it was available to be opened and it was opened."

He said it appeared there was a chain reaction and when one tile fell it was followed by the other 200. They had been installed by a sub contactor to the main contractor for a $10 million airport extension.

Mr Curley said the airport company accepted something had gone wrong and someone had to be accountable.

"It is a stock standard suspended ceiling system. Everyone uses it."

He said the damage from the falling solid plaster tiles was superficial.

One person was hit on the head and others were hit on the body.

The inquiry could take several days but the company wanted the entire area reopened as soon as possible to avoid delays.