A would-be suicide bomber's explosives failed to detonate in a packed church in western Indonesia during Mass on Sunday.

Police said he injured a priest with an axe before being restrained.

The 18-year-old assailant left a pew and ran toward the priest at the altar, but a bomb in his backpack only burned without exploding, said national police spokesman Maj Gen Boy Rafli Amar.

Before he was restrained by members of the congregation, the man managed to take an axe from the backpack and attacked Fr Albert Pandiangan, causing a slight injury to the 60-year-old priest's hand.