Passengers are told to expect delays after the shutdown and are advised to check with their carriers before coming to the airport.
Newark Airport in the greater New York City area has reopened after an unspecified emergency.
Anyone flying today should check with their airlines regarding flight schedules.
"I spoke with one of the emergency crews who told us that apparently, we had a flat tire and there was something about friction ... and that possibly there was smoke, and that's why we had to make the emergency landing".
Concerns as Merkel suffers new trembling spell on eve of G20
Ms Merkel, who has been German leader since 2005, was due to set off for Japan later on Thursday for the annual G20 summit. The chancellor has a reputation for stamina garnered in years of late-night domestic and European negotiating marathons.
Airport representatives could not immediately be reached for comment. The flight was then diverted to Newark.
"It's just a different set of situations", Boyd said by phone, adding that the forced emergency landing in the latest incident was another factor. He said was looking into getting another flight. About 45 minutes later, the airport was re-opened.
Flight 2098 took off from New York City's LaGuardia Airport bound for Houston and a short time later experienced hydraulic problems, prompting the emergency landing, Scott Ladd, a spokesman for the Port Authority of New York and New Jersey, said in an email.