Visitors blast around top exhibition on Sunday (6)
I believe the answer is:
guests
'visitors' is the definition.
(guest is a kind of visitor)
'blast around top exhibition on sunday' is the wordplay.
'blast' becomes 'gust' ('gust' can be a synonym of 'blast').
'around' is an insertion indicator.
'top exhibition on' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'sunday' becomes 's'.
'gust' going around 'e' is 'guest'.
'guest'+'s'='GUESTS'
(Other definitions for guests that I've seen before include "Folk receiving hospitality" , "Hosts entertain them" , "Invitees or hotel customers" , "Company" , "Those invited" .)