Lufthansa and several other parties had put in bids for parts of Air Berlin by today's deadline set by the administrator of the insolvent airline which employs more than 8,000 people.
Germany's second-biggest airline after Lufthansa filed for bankruptcy last month after major shareholder Etihad Airways withdrew funding following years of losses.
The German government promptly granted the airline a bridging loan of €150m to keep the airline flying during the administration process.
"The current status as of the 2pm deadline today is that we have received several offers that we will now have to assess in great detail," a spokesman for Air Berlin told Reuters TV, declining to provide further details.
A source close to the negotiations said the deadline for bids was not set in stone and that any offers made over the coming days would still be taken into account.
Most potential investors appear interested primarily in the airline's roughly 140 aircraft and its airport landing and take-off slots rather than in taking over the business.
Lufthansa made an offer for parts of Air Berlin, a spokesman said, declining to provide more detail.
A source familiar with the matter said Lufthansa planned to offer a three-digit millions of euros sum for up to 90 planes, including Austrian holiday airline unit Niki's fleet and 38 crewed planes it already leases from Air Berlin.
European budget airline EasyJet, which media reports had said was interested in acquiring up to 40 of Air Berlin's planes, only confirmed today that it had bid for parts of Air Berlin's short haul business.
"EasyJet has this afternoon submitted a proposal to the overseers of Air Berlin's insolvency to acquire parts of its short-haul business," the company said in a statement.
"The proposal is consistent with EasyJet's focused, city-based strategy in Germany. However, given a number of uncertainties associated with Air Berlin, there is no certainty at this stage that any transaction will proceed," the airline added.
Meanwhile former Formula One motor racing world champion Niki Lauda has put in a joint bid with German airline Condor, owned by holiday firm Thomas Cook, a spokeswoman for Lauda said.
He had told Austrian media that he would make an offer worth around €100m for Niki, an airline he once owned, and 17 Air Berlin aircraft. Thomas Cook declined to comment.
Separately German family-owned logistics firm Zeitfracht has offered to buy Air Berlin's cargo marketing platform, its maintenance business and regional unit LGW, which operates 20 Bombardier aircraft.
And aviation industry investor Hans Rudolf Woehrl has offered to buy Air Berlin in its entirety for €500m, to be paid in instalments, while China's LinkGlobal Logistics has asked to be given more time, until September 21, to formulate a bid.
A committee of Air Berlin's creditors is to discuss the bids on September 21 with a final decision on who to sell to pushed back to September 25, the day after Germany's federal election and four days later than previously planned.
Air Berlin was forced to cancel flights on two days this week after protesting pilots called in sick.