Police are searching two airliners at Atlanta's airport after receiving "credible" bomb threats, it has been reported.

According to an airport spokesperson, the threats were received against Delta Flight 1156, coming from Portland, Oregon, and Southwest Airlines Flight 2492, from Milwaukee.

US fighter jets escorted the planes into the Hartsfield-Jackson International Airport, US media reports.

Both planes landed safely and passengers were led from the aircraft. A bomb squad and sniffer dogs are in involved in the police search.

The bomb threats were reportedly made in an exchange on Twitter with Delta's customer assistance account.

A Delta customer assistance operative answered a user who appeared to be making the threats by saying: "We take all threats serious and have reported your comments to our corporate security team for further review/action."