North Korea has fired three short-range projectiles into the sea less than an hour before Pope Francis arrived for the first papal visit to South Korea in 25 years, South Korea's defense ministry has said.

The apparent test firing was conducted on Thursday from Wonsan on the North's east coast and flew about 220 kilometres, according to a ministry official who spoke on condition of anonymity, citing office policy.

The type of projectile has yet to be determined. North Korea did not declare a no-sail zone before firing the projectiles.

North Korea has a long history of raising itself to the top of its neighbours' and Washington's list of concerns.

The country has this year conducted an unusually large number of missile and artillery test firings. Pyongyang has expressed anger over ongoing annual military drills between the United States and South Korea.

Early on Thursday, on a dispatch carried by Pyongyang's official news agency KCNA, North Korea's Committee for the Peaceful Reunification of Korea urged Seoul to scrap the joint US-South Korea drills expected to start in coming days.

Pope Francis visit

Although North Korea declined an invitation to Seoul for the papal visit, Francis plans to reach out to Pyongyang during his five-day trip in a Mass for peace and reconciliation on the war-divided Korean Peninsula.

During his visit, Francis also plans to beatify 124 Korean martyrs and encourage a vibrant and growing local church seen as a model for the future of Catholicism.

At an airport just south of Seoul, the pope shook hands with four relatives of a South Korean ferry sinking that killed more than 300 and two descendants of Korean martyrs who died rather than renounce their faith.

Some elderly Catholics wiped tears from their faces, bowing deeply as they greeted the pope. A boy and girl in traditional Korean dress presented Francis with a bouquet of flowers.

The pope then stepped into a small, black, locally made car for the trip into Seoul, where he and President Park Geun-hye were expected to make speeches.