The St John the Baptist church in Maitland has been closed after 163 years because of falling masonry and concrete cancer.

Known as St John's Chapel, the 1846 Gothic church was claimed by the first bishop in the region, James Murray, as his cathedral in 1866 and features an ornate 20-metre-high square belfry.

Maitland-Newcastle diocese chancellor Beverly Zimmerman said the church was an important part of the region's history.

"The Catholics at the time did not have much but they worked together and raised money to build this church," she said.

"It was symbolic of the growing self-confidence of the Catholics in the area."

The chapel, in Cathedral Street, was vacated in 1933 for a larger provisional-cathedral in an old theatre nearby but remained at the centre of the Maitland-Newcastle Catholic Diocese until the headquarters moved to Newcastle in 1995.

During its lifetime the 300-seat church was used as a schoolhouse and parish hall.

When the diocese executive moved to Newcastle, its small parish returned to its pews.

Dr Zimmerman said countless baptisms, weddings and funerals had come before its altar.

New parish priest Father Matthew Muller described it as a beautiful building.

A diocese spokeswoman said engineers were looking at the building and would review its future.