TUI AG , co-owner of Hapag-Lloyd, has asked Chinese group HNA and Oman's Onyx Investments to make binding bids for a stake in the shipping group by late May, three people close to the process said.

While the suitors are currently conducting due diligence, Hapag is simultaneously preparing a prospectus for an initial public offering (IPO) based on first-quarter figures to put pressure on the bidders, one of the sources told Reuters.

But TUI, owner of tour operator TUI Travel , may be cutting it fine with initial plans to take Hapag public before the summer lull because it aims to delay until late May its decision on how to dispose of the holding.

"Like so often in these transactions, the deadline for the sale may have to be extended," another source said, adding that especially investors from the Gulf region were known not to rush investment decisions.

"I gauge the likelihood of a Hapag IPO in the second quarter as very low," a third person said, who is helping to organise the transaction.

TUI currently owns 49.8 percent of Hapag-Lloyd, but that stake is due to shrink in late May as it has agreed to sell an 11.3 percent block to co-owner Albert Ballin, a consortium of investors.

The third source said he believed that Hamburg-based Hapag-Lloyd would scrap plans to get a stock exchange listing if that sale went through.

HNA Group, China's fourth-largest airline group and parent of Hainan Airlines Co Ltd , as well as Onyx Investments Ltd, owned by the Oman Investment Fund, were not immediately available for comment.

A person close to Oman's government said Onyx was still waiting for an answer from Hapag to a tentative bid it had made.

A TUI spokesman said that while an IPO was still a possibility, "TUI is currently in talks with potential investors over the sale of shares in Hapag-Lloyd".

One sticking point, apart from price, is that the Albert Ballin investor group, which owns 50.12 percent of Hapag-Lloyd, is eager to restrict the influence of a potential new co-owner.

Albert Ballin is a group of Hamburg-based investors led by Klaus-Michael Kuehne, the majority owner of Swiss logistics group Kuehne & Nagel.

One source close to Hapag's owners said TUI hoped to split its entire stake between Onyx and HNA, keeping either investor below a blocking minority of 25 percent.

Albert Ballin is keen to keep Hapag headquartered in Hamburg and that no jobs are cut there. The investor group had been set up initially to prevent a sale of Hapag-Lloyd to Singapore-based Neptune Orient Lines in 2008.

TUI last month put on ice any decision on taking Hapag-Lloyd public after the earthquake in Japan and political unrest in the Middle East and North Africa upset markets.

TUI said earlier this month it had agreed to sell the 11.3 percent stake in Hapag-Lloyd to Albert Ballin in late May in a 315 million-euro ($460 million) deal prior to any sale or share flotation.

After that, its remaining stake would be worth 1.07 billion euros, based on the price agreed with Albert Ballin.

TUI, which started life as a mining and steel company in 1924, is expected by analysts to use the proceeds from any IPO or sale to buy back the shares it does not own in London-listed subsidiary TUI Travel , though it has never confirmed such plans. (Reuters)