Pol Maj-General Wichai Sangprapai, an adviser to the governor of Bangkok, said no force would be used against vendors who refuse to move to other locations, including those provided by the city, but those violating the Bangkok Metropolitan Administration (BMA) order will be charged under the law.
The flea market, famous for decades for its odd vintage goods, will be closed down after the area is cleared.
The BMA argued that it had received many complaints that the market, which occupied the footpaths and spilled out onto nine streets in the area, was interfering with road traffic and access to Central Hospital.
Wichai denied rumours that the BMA had sent people to harass the owners of some stalls. More than 200 vendors gathered in front of City Hall to demand an apology from Governor Sukhumbhand Paribatra.
They said they have been wrongly accused of trying to resist eviction from the flea market due to the money generated from the lucrative but illegal rental business.
Wichai alleged that the rent that the vendors had to pay for a spot on the footpath amounted to about Bt20 million per month and those opposing the order are involved with this illegal income-generating activity.