The Dutch authorities have confirmed the identities of five Turks and four Americans who perished in a jetliner crash at Amsterdam's Schiphol airport.

A Turkish pilots' group meanwhile blamed "wake turbulence" for the tragedy, describing the invisible, tornado-like currents caused by large jets that can hit a trailing airplane, especially a smaller one.

If the association's claims are proved correct, it would raise questions over whether air traffic controllers warned the pilot of the turbulence before the crash, which also left 80 crew and passengers with injuries.

"This appears to be the most significant possibility" for the cause of Wednesday's crash, association chairman Ali Ziya Yilmaz told a televised press conference in Istanbul.

Yilmaz said the association had obtained information that a Boeing 757, which he said has "the most dangerous wake turbulence," landed at Schiphol airport two minutes before the Turkish Airlines plane crashed.

Two Boeing employees, who just happened to be on the flight, and three crew members were among the nine fatalities whose identities were confirmed by the Dutch authorities on Friday.

"We have been able to establish their identities. We are not giving any further information," a Dutch official said, adding that the families had been informed on Thursday.

Authorities said the preliminary results of the official investigation into the black box recordings could be released next week when a team of Paris-based experts have finished their analysis.

"We have listened to the recordings, but the data must still be analysed," said Dutch Safety Board official Fred Sanders.

Yilmaz from the Turkish pilots' association said the Dutch authorities had highlighted the possibility of an engine failure without mentioning the wake turbulence scenario.

His group also called for an explanation of media reports that one of the pilots was still alive when rescuers arrived at the scene but was not given medical help.

The Boeing 737-800, en route from Istanbul to Amsterdam with 127 passengers and seven crew, crashed into a muddy field as it came in to land at Schiphol airport, breaking into three pieces.

Witnesses described seeing the tail hit the edge of a busy road and drag along the ground before the plane broke into pieces.

Turkish media has speculated that one of the assistant pilots, still a trainee, might have been in command of the plane at the time of the crash.

Pieter van Vollenhoven, who is leading the Dutch investigation, told the Dutch TV channel NOS that the incident was not the result of any violent or terrorist act.

"If that had been the case, we would have immediately informed the law enforcement authorities," he said.

Sixty-three people remained in hospital Friday, six in a critical condition.