Privately-owned Air Nigeria was part of Richard Branson's Virgin fleet until he pulled out in 2010, selling his minority stake.

It operated flights across West Africa and to London.

It is now shutting down operations and sacking over 500 staff in a move that has prompted union protests over alleged unfair dismissal and unpaid salaries.

The Nigerian Civil Aviation Authority suspended Air Nigeria in June due to financial concerns, although some flights were allowed to continue.

Several Nigeria airlines have folded in recent years due to lack of finance or poor safety.

"Corporations are like individuals, who naturally will get sick, and the usual thing to do is to admit them to hospitals, either for corporate surgery or for treatment, as the case may be," a statement from the company's Chairman Jimoh Ibrahim said.

Ibrahim said Air Nigeria would close operations for at least a year but he hoped to resurrect the airline in the future.

Dana Air flight 992, a McDonnell Douglas MD-83 (BA.N), crashed into an apartment block in a populated Lagos suburb in June, killing 153 people onboard and 10 others on the ground.

Air crashes are relatively common in Africa's most populous nation, although Air Nigeria was never involved.

The aviation ministry cleared Dana to fly again last week even though the accident bureau has not concluded its investigation into the crash. (Reporting by Joe Brock; Editing by Tim Cocks and David Cowell)

• A Permanent Economic Emergency