The traders were returning to their neighbourhood after buying vegetables from the wholesale market in Manikganj’s Jaagir.
They entered the offices just after Saturday midnight, bdnews24.com's Chief Political Correspondent Sumon Mahmud reported from the scene.
Around 12:45am on Sunday, police drove out eight men who had been staying there.
Police locked it down and took away the keys as well, Mahmud added.
The incident took place a day before the anniversary of the last general election which the BNP boycotted.
The party is planning a rally in Dhaka to protest on the day but are yet to get police permission.
Around midnight, detectives picked up party's Joint Secretary General Ruhul Kabir Rizvi from there.
Both the detectives and Paltan police said he had not been arrested.
They said Rizvi had been taken to a hospital for treatment.