No new radio signal has been received from an EgyptAir jet since the day it crashed in the Mediterranean last week, sources close to the investigation said on Friday.

Media reports on Thursday suggested that a new signal had allowed officials to further home in on where the black box recorders might be located.

But the sources told Reuters that nothing new had been detected since a radio signal picked up on the day of the crash from the plane's emergency locator transmitter (ELT) which allowed officials to determine a broadly defined search zone of 5 km (3 miles) in radius.

"There has been nothing since day one," one of the sources said.

More than a week after the Airbus A320 crashed on May 19 with 66 people on board, including 30 Egyptians and 15 from France, investigators have no clear picture of its final moments.

Search teams are working against the clock to recover the two flight recorders that will offer vital clues on the fate of flight 804, because the acoustic signals that help locate them in deep water cease transmitting after about 30 days.

France's BEA air crash investigation agency said French naval survey vessel Laplace had left Corsica on Thursday and was heading toward the search zone north of the Egyptian port of Alexandria.

A French official said the vessel would arrive on Sunday or Monday.

The vessel contains equipment from ALSEAMAR, a subsidiary of French industrial group Alcen, which can pick up black-box pinger signals over long distances up to 5 km (3 miles), according to the company's website.

These are separate from the signals transmitted by the ELT, which sends a radio signal upon impact that is not designed to continue emitting once the plane is submerged underwater, said one of the sources close to the investigation.

The French vessel will conduct a deepwater search in "four or five" areas within the 5 km search zone believed to contain the two black boxes, with the possibility of expanding the zone should nothing be detected, said another of the sources. – Reuters