(WJW) — Flights are “resuming gradually” Wednesday morning at Cleveland Hopkins Airport as the Federal Aviation Administration lifted a ground stop due to nationwide outages of a system that provides key safety information to pilots.

The FAA announced at around 6:30 a.m., they were still working to fully restore the Notice to Air Missions system following an overnight outage.

At around 7:30 a.m., the FAA ordered airlines to pause all domestic departures until 9 a.m. Eastern Time to allow the agency to validate the integrity of flight and safety information,” a tweet said.

Nearly 5,000 flights nationwide were delayed and almost 900 were canceled by around 10 a.m.

The ground stop was lifted just before 9 a.m.

Before commencing a flight, pilots are required to consult NOTAMs, or Notices to Air Missions, which list potential adverse impacts on flights, from runway construction to the potential for icing. The system used to be telephone-based, with pilots calling dedicated flight service stations for the information, but has now moved online.

Here’s a look from SkyFOX over Hopkins Airport in Cleveland where flights were grounded:

The White House said “there is no evidence of a cyberattack at this point, but the president directed DOT to conduct a full investigation into the causes,” according to a tweet.

According to FAA advisories, the NOTAM system failed at 8:28 p.m. Eastern on Tuesday preventing new or amended notices from being distributed to pilots. The FAA resorted to a telephone hotline in an effort to keep departures flying overnight, but as daytime traffic picked up it overwhelmed the telephone backup system.

Air Force spokesperson Ann Stefanek said the U.S. military flights were not impacted because the military has its own NOTAMS system separate from the FAA system and the military’s system was not affected by the outage.

The FAA continues to look into the cause of the initial problem.

Click here for flights in and out of Cleveland Hopkins Airport. Click here for your flight status at Akron-Canton Airport. Delays are expected to linger throughout the day Wednesday.

Stay with FOX 8 for developments.