At least five bomb threats were made Tuesday against flights leaving from or landing in the United States, according to a report.

The threats, which were phoned in, were not deemed credible, NBC News reported, citing government sources.

It prompted a police bomb squad with search dogs to scour a US Airways flight when it landed at Philadelphia International Airport about 6:15 a.m.

Authorities had received a threat saying there were multiple devices aboard while the plane was en route from San Diego.

They found no signs a bomb was on the Airbus A320 carrying 88 passengers and five crew members.

Four of the five flights which received threats — from US Airways, Delta Air Lines, United Airlines and the Mexican carrier Volaris — have landed safely, according to NBC News.

A Korean Air Flight 23 from Seoul to San Francisco was scheduled to land Tuesday afternoon.

The hectic day for airliners was made worse when all United Airlines flights were temporarily grounded Tuesday morning for separate technical issues.

United delayed flights at 8 a.m. due to "automation issues."

The halt lasted about 39 minutes until officials could "ensure aircraft departed with proper dispatching information," United Airlines spokesman Charles Hobart said.