Pope Francis on Thursday appealed for Catholics in Indonesia to engage with people from other faiths in a message of religious unity to an open-air stadium mass of nearly 80,000 people.

"I encourage you to sow seeds of love, confidently tread the path of dialogue, continue to show your goodness and kindness... and be builders of unity and peace," he told devotees in capital Jakarta.

The pontiff arrived for the mass in a tactical vehicle built by an Indonesian state-run defense company.

Religious unity was the key theme of his three-day visit to the world's most populous Muslim-majority country.

Earlier on Thursday he signed a declaration with the grand imam of Jakarta's Istiqlal Mosque.

The mass was the final act of a packed first stop on the longest trip of his papacy as he tried to energize the local faithful who represent around three percent of Indonesia's population.

The grueling 12-day tour will head to Papua New Guinea, East Timor and Singapore when he departs Jakarta on Friday.

Devotees poured into the stadium compound hours early after arriving on packed buses, many wearing pope t-shirts and taking group photos with the huge structure in the background.

—With reports from Wendy Palomo