The bankruptcy of German airline Air Berlin last October caused a notable drop in domestic air traffic in Germany in the first months of 2018, the country's Airports Association (ADV) said Saturday.

For the first five months of 2018, the ADV reported a 5 percent decrease in passengers for domestic connections compared with the same period last year.

"German airports are still feeling the consequences of the comprehensive consolidation measures at the airlines, in particular the cessation of one Air Berlin," said ADV Chief Executive Ralph Beisel.

However, the strong growth of inter-European traffic still ensured an overall increase in passengers at German airports.

According to the ADV, 22.44 million passengers used German airports in June, a 2.4-percent increase compared with the same month last year. This overall growth was modest because of the decline in domestic traffic, the association said.

Following Air Berlin's bankruptcy in October 2017, Lufthansa subsidiary Eurowings and British low-cost airline Easyjet have gradually begun to offer replacement domestic services in Germany.

The drop in traffic has been particularly notable at smaller airports such as in Erfurt (49.8 percent less traffic in June than during the same month in 2017), Karlsruhe (73.1 percent less) and Nuremberg (29.3 percent).

However, airports in Berlin and Dusseldorf have also yet to fully recover from Air Berlin's cessation.

Preliminary calculations show that overall passenger numbers increased by 2.3 per cent in the first five months of the year compared with the same period in 2017, to just under 110 million passengers.