Mai Ahmad Fatty said financial experts were trying to evaluate the exact loss.
BBC reports that luxury cars and other items were reportedly loaded on to a Chadian cargo plane as Mr Jammeh left the country.
Mr Jammeh has not commented and the BBC has not independently verified the claims.
After 22 years in power, Mr Jammeh flew into exile on Saturday.
He had refused to accept election results but finally left after mediation by regional leaders and the threat of military intervention.
President Barrow remains in neighbouring Senegal and it is not clear when he will return.
However, West African troops entered the Gambian capital, Banjul, on Sunday to prepare for his arrival.
Cheering crowds gathered outside the State House to watch soldiers secure the building.