Flights were delayed or cancelled at Newark airport due to telecommunications, equipment and “staffing” issues at the Philadelphia air traffic control center.

The Federal Aviation Administration said a series of issues prompted it to dramatically slow traffic at Newark Liberty Airport on Monday, prompting United Airlines to divert at least 35 flights to other airports.

The FAA issued a ground stop for Newark-bound flights around 1:53 p.m. due to an equipment failure. Departures headed to Newark were held at their origin airports through at least 5 p.m., officials said.