The reserve's management board said on September 11 it had received a report from a tourist who spotted small rocks and debris falling inside Doi Cave, or Bat Cave, in Kho Muong Village, Pu Luong Commune.
The visitor also reported large rocks overhead that appeared at risk of falling, potentially endangering tourists.
The management board said the concerns required urgent inspection as they could pose a threat to visitors' safety.
Tours to the cave are currently organised by the local community in Kho Muong Village, which also charges admission fees. The activities have not been authorised by the relevant authorities, according to the board.
It has asked Pu Luong Commune authorities to immediately suspend tours and other visitor activities at the cave until safety inspections are completed and measures to address any risks are approved.
The village has also been asked to stop collecting admission fees and providing services related to cave tours during the inspection period.
Authorities plan to survey the cave's geological and terrain conditions, assess rockfall and landslide risks and identify areas that could pose a danger to visitors.
Depending on the findings, measures could include restricting access to hazardous areas, stabilising unsafe sections, installing warning signs and controlling entry to the cave.
Local residents, tourism businesses and visitors will also be warned not to enter the cave until authorities declare it safe to reopen.
The management board said further inspections would be carried out to prevent unauthorised tours and review admission fees and tourism services at the site.
Bat Cave was formed in limestone about 250 million years ago and is linked to an underground river system. It stretches about 2.5 kilometres and has an entrance more than 10 metres high.
The cave is part of a karst landscape formed by the erosion and dissolution of limestone.
