The Pope posed and smiled for a selfie with a young Catholic in South Korea.
Pope Francis was greeted by cheers and the waving of handkerchiefs as he arrived at South Korea's Daejeon World Cup Stadium to hold a mass.
Newly-released video reveals the harrowing final moments of a group of teenagers on the ship as it capsized.
Vast crowds gathered in Seoul's Gwanghwamun Square in South Korea as Pope Francis delivered a beatification mass for 124 Catholic martyrs.
Beatification is the last step before sainthood in the Roman Catholic Church.
In his homily before a crowd of hundreds of thousands, Francis said the martyrs' courage and charity and their rejection of the rigid social structures of their day should be an inspiration for people today.
Pope Francis has surprised South Koreans during his visit to the country by shunning an expensive luxury car to travel in a compact car instead.
After arriving at the airport he climbed into the backseat of a a Kia Soul - the manufacturer's second smallest model.
Pope Francis has refused to use a bullet-proof "popemobile" like his predecessors in favour of low-key cars.
His choice of car has received wide coverage in South Korea, where ostentatious shows of wealth usually represent a person's status.
Pope Francis has arrived in South Korea on the first papal visit to the Asian nation in 25 years, stepping off a plane on to a red carpet and greeting the president, Catholics and grieving relatives of the recent ferry disaster.
During his five-day visit, Francis plans to beatify 124 Korean martyrs and encourage a vibrant and growing local church seen as a model for the future of Catholicism.
North Korea has fired three "short-range projectiles" into the sea, just an hour before Pope Francis arrived in South Korea for an official visit, Associated Press have reported.
An official with the South Korean Defence ministry said the apparent test firing Thursday came less than an hour before rival Seoul welcomed the pope for the first papal visit to South Korea in 25 years.
The official says that the projectiles were fired from Wonsan on the east coast and flew about 220 kilometers (135 miles).
The official spoke on condition of anonymity, citing official policy.
Young survivors of the South Korean ferry disaster have begun giving testimony at the trial of the 15 crew members charged with abandoning the sinking ship.
The children, whose identities have been protected, said they were repeatedly told to stay in their cabins when the ship began to take on water.
"We were waiting and, when the water started coming in, the class rep told everyone to put on the life vests ... the door was above our heads, so she said we'll float and go through the door and that's how we came out," one of the teenagers said.
Others told the hearings that coastguard officials waited outside the stricken ferry for passengers to swim out rather than go into the ship to try and rescue them.
"We said to ourselves, 'why aren't they coming in?'" one said.
The crew members on trial, including the captain, have said they thought it was the coast guard's job to evacuate passengers. Video footage of their escape triggered outrage across South Korea.
South Korean police has said that a body found last month in the south of the country belonged to a fugitive businessman who headed the family that owned the operator of a ferry that capsized in April, killing more than 300 people.
Police said at a press conference that a badly decomposed body found on June 12 had been identified by DNA evidence as well as fingerprints as that of Yoo Byung-un, who had been the subject of the country's largest manhunt.
North Korea fired two short-range missiles into its eastern waters, a South Korean official said. The apparent test fire that comes just days after the country tested what it called new precision-guided missiles.
The Seoul defence ministry official said the missiles were fired from Wonsan in Gangwon Province and are presumed to be short-range ballistic missiles.The official said North Korea fired the missiles without designating no-sail zones, which the South Korean military views as a clear provocation.
South Korean media quoted officials as saying the projectiles appeared to be Scud missiles. North Korea regularly test-fires missiles and artillery, both to refine its weapons and to express its anger over various developments in Seoul and Washington.
Crew members from the sunken South Korean ferry have arrived at a court in Gwangju, the closest city to the scene of the disaster, to face charges ranging from negligence to homicide.
Captain Lee Joon-seok was escorted in handcuffs to the court along with the 14 surviving crew members responsible for the ship's navigation.
Lawyers and prosecutors are today expected to begin their arguments and start questioning defendants.
Captain Lee Joon-seok, 68, and three senior crew members have been charged with homicide, and could be sentenced to death.
Two were charged with fleeing and abandoning ship, which carries a maximum sentence of life imprisonment. Nine were charged with negligence, which can carry jail terms.