Unister, the holding company behind a string of high-profile online travel brands in Germany, has made itself voluntarily insolvent.

Under its umbrella are Fluege, Reisen and Geld - all of which will not be affected, according to the filing, as they operated independently by other entities.

An insolvency fund will allow the business to continue operations whilst a new owner for the company is found.

The development comes just days after the death of CEO Thomas Wagner and his co-founder Oliver Schilling in a plane crash.

The pair - and two other passengers aboard the Piper-32 aircraft - were flying from the north Italian city of Venice to Unister's home city of Leipzig.

Stories in the German media claim the two founders were returning from a business trip in Venice, where they had been meeting potential investors.

Various reports have also suggested large quantities of money were found at the crash site.

The threat of insolvency has hung over Unister Holdings for quite some time, with the company looking for a buyer since 2014.

The company was, in November 2015, said to be making attempts to find some form of capital to keep the company in good shape, as well as also considering a spin-off of the Unister Travel consumer brands.