An intruder broke into the former royal palace last night and broke irreplaceable oriental vases and a mantel clock dating from the French second empire.
Alarms sounded in the building, built by the Prince Regent in 1783 as a summer home, but the damage had been done by the time the intruder was caught.
Detective Inspector Graham Cox, of Sussex Police, said: 'This appears to have been a case of wanton damage.'
Ann Kenny, head of public services at the pavilion, said many of the damaged exhibits could not be replaced at any price and that the real cost was to the historical standing of the building, which attracts 340,000 visitors a year.
'The staff are in a state of shock and obviously it is something that is exceedingly upsetting,' she said.
'Most of our exhibits are unique and obviously they can't be replaced.'
She said the Royal Pavilion was a matchless building with its Indian decoration on the outside and Chinese on the inside. 'It is very, very splendid - one of the most exotic and beautiful buildings in the United Kingdom.'
A 28-year-old unemployed man from Hove, East Sussex, is being questioned by detectives in connection with the incident.