The 15th Century moated manor house is owned by the National Trust and visited by thousands each year.
Caroline Pons, the trust's assistant director of operations, said: 'Nobody was hurt, but for safety reasons we've made the decision to close the hall and inner courtyard, whilst we investigate and make the area safe.
'For the safety of our visitors, staff, volunteers and family who live onsite, we've decided to close Oxburgh Hall whilst we work with experts to investigate the damage caused by the dormer window collapse.
'We need to understand the cause, survey the wider area for damage and make the building safe and water tight once more. We hope to re-open as soon as we can, but only when it's safe to do so. In the meantime, visitors are welcome to enjoy the grounds.'
Fire alarms were set off by the shock of the collapse, which sent tonnes of masonry crashing down. Crews were on-site for two hours surveying the damage.
Structural engineers and surveyors have now taken over, checking that two other gable windows in the same wing are sound.
Jo Bosch - the trust's manager at Blickling Hall - was at Oxburgh yesterday, helping staff break the news to visitors that they could not see inside the property.
'This was built in 1500 and these things do happen,' she said. 'You can't forsee all the problems with buildings of this age.'
Built by Sir Edmund Bedingfeld, Oxburgh Hall has had a rich. A secret chamber was built by its catholic owners to ensure their priest would be safe in the event of a raid during the 1560s, when Elizabeth I passed laws suppressing their faith.
It is also houses tapestries sewn by Mary, Queen of Scots after she was imprisoned by Elizabeth. While Mary was not imprisoned at Oxburgh, her needlework was aquired by the Bedingfeld family in the 1760s.
Today the preserved house is little-changed from those times. Swans glide on its moat, while its rooftops offfer views of Ely Cathedral.
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