Four of the 19 injured from the Madrid jet disaster were in "very serious" condition in hospital on Thursday, while a Spanish minister said it would take two days to identify all the bodies of the 153 dead.

A spokesperson for the regional health authority told AFP that 19 people were in different Madrid hospitals.

Four were in "very serious" condition, six were "serious", eight were said to be improving and one suffered a light injury.

An MD-82 belonging to budget airline Spanair crashed after a failed takeoff at Madrid's Barajas airport on Wednesday, killing 153 people and leaving 19 others injured.

Transport Minister Magdalena Alvarez said it would take two days to identify all the victims, many of whom were badly burned.

"Up to now they have been identified with their fingerprints and in certain cases by there will have to be DNA tests," the minister said on national radio.

Alvarez said that Spanair's ground technicians had approved a second takeoff attempt after the pilot returned to the terminal complaining of a problem.

"In the first attempt, the pilot came out but returned because he detected something, which will have to be determined by commission of inquiry," Alvarez said.

"The maintenance officials of the company concerned authorised the takeoff, assuming their responsibility which is precisely to examine the plane when the captain signals any kind of incident," the minister added.

Asked whether there was any kind of negligence involved, Alvarez replied: "I would not dare say that.

"It is above all the black boxes that will allow us to determine the causes," she said.

AFP