Hundreds of parishioners watched in shock as a Catholic priest died at the altar during mass, moments after baptizing a baby.

Napier's longest-serving priest, Monsignor Timothy Francis Hannigan, 81, collapsed at the altar during communion at St Patrick's Catholic Church on Sunday.

A doctor and nurses in the packed church rushed to help the popular priest when he slumped to the ground about 9.30am, but he died by the altar of the church where he had served for more than 30 years.

"It's one thing for a priest to die in a church, but it's a whole other thing for him to die during communion," a parishioner who did not wish to be named said yesterday.

The congregation continued to pray as his body was taken away. Some also recited a rosary.

Former St Patrick's parish priest Father Paul Kerridge said Monsignor Hannigan had taken mass as usual, and had just finished baptising a baby and blessing the parents when he fell to the floor.

It was believed he died after a cardiac arrest.

The energetic priest had not shown any previous signs of illness, and was fine during the sermon, Father Kerridge said.

His loss would be keenly felt.

"I would say everyone in the parish would consider him their next of kin. He was like a brother."

Parishioner Ross Allan said those who were there were shocked by what they saw unfolding.

"One moment he had baptised a child ... then the next moment there was all this commotion up the front of the church. It was a very unusual situation."

Monsignor Hannigan was a pillar of the community who did everything he could to help those in need, including the homeless who showed up on his doorstep, Mr Allan said.

Fellow parishoner and retired Napier dentist David Marshall  said church members were comforted by the fact that Monsignor Hannigan did not have to suffer a long illness.

‘‘He died doing what he did best, which was saying mass for his parish family – which I think is the greatest gift a priest could have.’’

One of the highlights of Monsignor Hannigan's services was his blessing of children, he said.

In a now-famous incident, a visiting bishop had once been completely ignored when all the kids flocked to Monsignor Hannigan.

"There he was waiting for children to rush up to him, and they all rocketed straight past. He was left quite nonplussed."

Monsignor Hannigan had officiated at thousands of wedding ceremonies, funerals and christenings.

Originally from Ireland, he emigrated to New Zealand in 1956. He worked as a priest in Wellington, Levin, Palmerston North and Ohura before moving to Napier to become parish priest at St Patrick's in 1979.

He was made a member of the New Zealand Order of Merit in 2000 for services to the community, including his work with the sick and elderly.

At the time, he attributed the award to his parish and joked that he "thought they'd got the wrong person".