DUBLIN, June 28 (Reuters) - Groups representing Europe's largest airlines and airports have warned of chaos and hours-long queues unless countries better coordinate the roll-out of the EU's digital COVID-19 certificate and ensure passengers are processed before arriving at airports.  

The European Union's system of digital COVID-19 travel certificates is due to come into force on Thursday, but airports group ACI and airlines representative bodies A4E, IATA and ERA warned in a letter to EU national leaders of a "worrying patchwork of approaches" across the continent.  

"As passenger traffic increases in the coming weeks, the risk of chaos at European airports is real," the groups said in the joint letter sent on Monday and seen by Reuters.