The mishap occurred when the concreting work of a new structure of the St Augustine Church came crashing down, causing injuries to workers on the spot.
One worker, suspected to be a migrant labourer from Odisha, died on the way to a private hospital in Kochi, a hospital spokesperson said.
Search and rescue operations are on as some workers were suspected to be trapped in the debris as the concrete roof collapsed with the iron roads jutting out.
State Revenue Minister Adoor Prakash said the district authorities in Alappuzha and Ernakulam have been instructed to rush more fire department and rescue personnel to search for survivors in the rubble.