They filed into a small side-chapel for the mass, which was broadcast live on Catholic TV network KTOTV.
Up to 150 workers have been working at the cathedral daily since the fire, continuing to remove debris and stabilise the structure.
Less than 10 per cent of the 850 million euros ($A1.4 billion) pledged by billionaires, business leaders and others has been received so far, the French government said.
It will take place at 6:00 pm (1600 GMT) in the Chapel of the Virgin on the east side of the cathedral behind the choir, which has been confirmed to be safe.
The mass, marking the annual anniversary of the consecration of the cathedral's altar, came exactly two months after the fire destroyed its spire and the oak-framed lead roof.
Among the high-profile people who promised to donate to the rebuilding effort were luxury goods tycoons Bernard Arnault and François-Henri Pinault.
"It is a nice symbol".
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"There could be people who promised to donate then in the end did not", Riester told France 2 television, without giving further details.
French President Emmanuel Macron's timeline to rebuild Notre Dame, which dates back to around 1260 but has been modified, is five years, though Riester said that perhaps it may take longer. 'But more importantly, and this is normal, the donations will be paid as restoration work progresses'.
This comes as the French parliament is slowly passing back and forth amendments to a new law that would create a "public body" to expedite the restoration of the cathedral and circumvent some of the country's famously complex labor laws.
"The president was right to give a target, an ambition", he said.
While the clean-up and consolidation work now underway is hugely important, it does not fit that description, said another foundation official, speaking on condition of anonymity.
If the authorities approve the plan, the idea is to celebrate the evening prayers on the parvis, the diocese said.
The damaged cathedral. fix work is underway, but it expected to take years.
"We hope that in five years the cathedral will be reconstructed, and I'm convinced that we will be able to meet this deadline without too much difficulty".