By Alexander Hübner and Kirsti Knolle
MUNICH/VIENNA (Reuters) - Niki airline administrator will start talks on Thursday to find a buyer for the insolvent Austrian carrier, formerly a unit of collapsed Air Berlin, after a deal with Lufthansa fell through.
A spokesman for the administrator said the carrier would in a few days lose its valuable runway slots, one of the most attractive assets for possible buyers, which means the clock is ticking on sales negotiations.
Lufthansa had signed a 210 million euro (184.7 million pounds) deal in October to take over large parts of Air Berlin's assets, including Niki.
But the German flagship carrier abandoned plans to buy Niki on Wednesday due to competition concerns, grounding the Austrian unit's fleet and stranding thousands of passengers in what its Managing Director Oliver Lackmann said was a "national disaster for Austria".
Three to four parties are now interested in taking over Niki, Wolfgang Katzian of Austrian union GPA told broadcaster ORF earlier on Thursday, fanning hopes for about 1,000 workers whose jobs hang in the balance.
Before Air Berlin was carved up in October, former motor racing driver and Niki's founder Niki Lauda offered around 100 million euros jointly with Thomas Cook's airline Condor for Niki plus 17 aircraft.
He told ORF radio on Thursday that he was still interested but would try to take over Niki without a partner this time.
British Airways parent IAG has dropped out of the bidding.
Austria's Transport Ministry estimated that about 5,000 Niki passengers could be stranded in the next two weeks. Many of them will be able to fly home on other airlines, but the ministry has started talks to charter some capacity.
German industry body BDL said German airlines would also help return Niki passengers home by offering them available seats on their flights at "rescue fares".
(Additional reporting by Victoria Bryan; Writing by Maria Sheahan; Editing by Michael Shields and Edmund Blair)