North Korea's trash balloon campaign, missile launches and the emergence of GPS "spoofing" have increased risks in South Korean airspace, aviation experts say, complicating airline operations as tensions rise between the rival nations.

In late May, North Korea began floating thousands of balloons with bags of trash, including human excrement, suspended under them into South Korea, in what analysts say is a form of psychological warfare.

Hundreds of balloons landed in the South during seven waves between May 29 and June 27, including one on a runway at Incheon airport, forcing a three-hour suspension of takeoffs and landings at its biggest international gateway.

When the balloons first appeared, aviation navigation interference from North Korea also spiked, including what appears to be the first bout of so-called "spoofing" affecting commercial aircraft in the South.

"Airspace safety is gradually deteriorating," OPSGROUP, a membership-based organisation that shares flight risk information, said in a June bulletin. "There are no official airspace warnings for South Korea, but the risk situation seems to be getting worse."

South Korea's transport ministry said its military, air traffic control authorities and airlines maintain a 24-hour surveillance and communication system.

"The South Korean military detects these balloons using surveillance assets… day and night," a military spokesperson said, without giving further details.

North Korea, which also launched trash balloons in 2016, says they were retaliation for propaganda campaigns by North Korean defectors and activists in the South who send items via balloon.