"The European Commission has been working day and night to try and be sure that we are able to open the airspace bit by bit and do it in a gradual and a safe way," Flynn said.
European Union officials had been receiving increasing pressure from the aviation industry, which is losing an estimated $200 million in revenue per day due to the grounding.
Officials from across Europe agreed on Monday to create three zones for flying over Europe -- a no-fly zone over the ash cloud, a caution zone in nearby areas "with some contamination," and an open-skies zone. Planes flying in the caution zone will need to be checked for engine damage.
For those passengers lucky enough to be on the first flights out, elation at finally getting in the air was only tempered by a fear of what the ash might do.
"I was very nervous," Lufthansa passenger Dominique Burkhard said of his Los Angeles to Frankfurt, Germany, flight. "One time we had turbulence. This was not so funny."
Unable to take to the skies, the British government hoped to ease waterborne escapes from the island by suspending the "Titanic Laws," allowing ferries to carry more passengers than would normally be legal.
It's the first time such a measure has been taken since the laws' implementation more nearly 90 years ago after the Titanic disaster in 1912. Dozens died after the massive ship's fateful run-in with an iceberg partially because there were far too many passengers for the number of lifeboats on the ship.
For Americans, home is a lot farther than a ferry ride away and the U.S. State Department said it had no plans to evacuate citizens by air or water, noting that by the time an evacuation could be organized, commercial flights would likely be available.
For those who have run out of money while stranded abroad, the State Department said it had a "limited amount of emergency loans that may be made available" under some circumstances and will help people send money to stranded loved ones.
ABC News' Maeva Bambuck, Kirit Radia and the Associated Press contributed to this report.