Ryanair logged Monday a 306-million-euro third-quarter net loss on virus fallout, warning also of a huge annual loss in "the most challenging year" in its 35-year history.

The Irish no-frills airline's loss after taxation in the third quarter or three months to December, contrasted sharply with net profit of 88 million euros a year earlier.

"Covid-19 continues to wreak havoc across the industry," Ryanair said in a results statement.

"Christmas and New Year traffic was severely impacted by UK travel bans imposed at short notice by many EU governments on December 19 and 20."

Passenger numbers tanked 78 percent in the reporting period to just 8.1 million people. That compared with 35.9 million last time around.

"FY21 will continue to be the most challenging year in Ryanair's 35 year history," the company added.

Ryanair forecast an annual net loss of between 850 million euros and 950 million euros, despite the ongoing rollout of vaccines.

The most recent lockdowns and restrictions were predicted to slash annual traffic to between 26 million and 30 million people. That compared with prior guidance of up to 35 million.

"The third quarter has obviously been heavily influenced by the continuing Covid travel restrictions," said Chief Executive Michael O'Leary in a video accompanying the earnings release.

"We had expected that things would continue to recover in Q3 -- but in the week before Christmas the emergence of the UK and South African variants led to further severe travel restrictions, particularly in flights to and from the UK, and that had an adverse impact on the Q3 numbers."