Investigations began after the school's leaders were made aware of one allegation on Wednesday.

It was reported the same day and a staff member was immediately placed on administrative leave.

In a statement, the Catholic Diocese of Maitland-Newcastle said a connected but "very separate" allegation of a different nature against another staff member came to light on Thursday. Those allegations have since been reported to the relevant authority and that staff member has also been placed on administrative leave.

"Due to the nature of the investigations now under way, the Catholic Diocese of Maitland-Newcastle cannot provide any further comment at this time," the statement said.

"When able, the diocese will provide further information to members of the All Saints' College community.

"The Diocese of Maitland-Newcastle responds to all allegations of abuse and takes safeguarding seriously and places the safeguarding of children and vulnerable persons first."

It's unclear at this time what "serious misconduct" the allegations against the two teachers refers to.

It comes weeks after the diocese released a report which found Catholic schools and parishes across the Hunter were meeting key safety requirements to protect children and adults at risk of abuse.