Businesses in Grimsby are counting the cost after a bomb scare forced a main shopping thoroughfare to close.
A man threatened staff at Freeman Street Post Office and left a parcel inside before leaving on Wednesday.
Shops were sealed off and people evacuated while a controlled explosion was carried out.
Businesses estimate their loss of earnings could run into thousands of pounds. Police are appealing for witnesses to come forward.
A police spokesman said the man, who was carrying a BHS carrier bag, demanded cash from Post Office staff.
When he did not get the money he made threats before leaving the package on the counter.
He was seen heading towards Riby Square.