Travellers who pitched their caravans on a Kingston recreation ground may be there for days, according to the leader of the council.
Five caravans drove through a gate yesterday and spent the night in the Fairfield recreation ground.
Derek Osbourne, leader of Kingston Council, said there was a pregnant woman and a child who may have measles among the group.
He said: "It is totally unacceptable that the Fairfield is being occupied in this way.
"Security officers have been put in place to make sure no-one else enters the premises.
"Once we have carried out welfare checks on people in the camp we will make every effort to remove them."
The Fairfield Recreation Ground is next to the town centre behind the Cattle Market and the Kingfisher leisure centre.