The Mainshill Wood Solidarity camp was established by opponents of plans for the mine near Douglas, South Lanarkshire.
Strathclyde Police said they arrested 14 men and five women yesterday after moving on to the site at 8:30am. Campaigners, who have spent six months building barricades, treehouses and tunnels, said sheriff officers and up to 30 police officers arrived.
Scottish Coal has been given permission to mine about 1.7 million tonnes of coal from the Lanarkshire site.
Those occupying the site have said they will stay as long as possible, and resist any attempts to remove them.
One protester, "Doug Well", who is resisting eviction in a fortified tunnel, said: "We've been here for so long now, and we really don't want to leave. If this mine goes ahead, it really will be a tragedy for the local people and for the climate.
"I'm going to do everything I can to make it as hard as possible for them to remove me."
Another protester called Richard, who would not give his surname, described the scene.
He said: "The officers are dismantling the tree house around the protester but the person will be locked to it or locked to the person next to them, so they will have to cut their way through and winch that person down.
"This is a peaceful protest but we are here to stop this mine or make open-cast mining as difficult as it should be, so nothing is going to get us out of the camp except other people using force against us."
He said about 60 campaigners were at the site, with 40 in tree houses or tunnels.
The camp in Mainshill Wood is on land belonging to Douglas & Angus Estates, which was granted a warrant to evict the protesters on 29 June.
A police spokeswoman said officers were not directly involved in the removal of the protesters.
She said: "Strathclyde Police is not part of the formal eviction process. However, they are there to support the process should they be required to do so.
"Our officers are there to protect the safety of those present at the site and to facilitate the right to peaceful protest. However, should anyone be observed committing a criminal offence, the appropriate action will be taken."
Green MSP Patrick Harvie condemned the move. He said: "Local residents around Mainshill are facing a blight on their lives that will last for years and, like them, I support the campaigners."