Five Turks and four Americans were killed when a Turkish Airlines jet crashed into a field short of the runway at Amsterdam's Schiphol airport on Wednesday, an official said on Thursday.

Haarlemmermeer Mayor Theo Weterings said officials were also trying to identify the rest of the passengers on flight TK 1951 from Istanbul, especially those who were seriously injured.

Sixty-three people are still in hospital, including six in a critical condition, he told reporters.

"Four of them are in such a severe condition that we have not been able to communicate with them," Weterings told a news conference.

Three of the nine people killed were Turkish crew.

Investigators are examining the flight recorders from the Boeing 737-800, which were taken to Paris where French authorities were providing technical assistance.

A reconstruction of the accident will be made in combination with data from the recorders and information gathered at the scene, Dutch Safety Board spokeswoman Sandra Groenendal said.

"We will know more after the weekend and probably have clues to determine the direction of the investigation and how to proceed," she said.

The mayor said authorities now believed 135 people had been on board, not 134 as previously thought, of whom 121 people were treated in hospitals around Amsterdam.

The plane was carrying mainly Dutch and Turkish nationals, as well as Britons and Americans.

The flight from Istanbul slammed into the field in light fog while trying to land at Schiphol and passengers described the plane as suddenly dropping to the ground during landing.

Safety Board chairman Pieter van Vollenhoven told Dutch media the plane left a short trail in the field where it crashed, indicating the engines might have stopped providing forward thrust.

"If you then lose speed, you then literally fall out of the sky," he was quoted saying.

Three staff from Boeing, the plane's manufacturer, and two investigators from the manufacturer of the engines, CFM International, are assisting Dutch authorities. Turkish Airlines will provide maintenance records of the plane.