Adverse possession happens when someone, who is not the owner of the land, has taken over possession of land or property for an acceptable period of time; he/she is entitled to acquire a possessory interest in the property unless the paper owner or other possessors can prove a better and older title against him/her.
According to section 7 of the Limitation Ordinance, the adverse processor has to prove the possession of 20 years where the action started before 1 July 1991, or a period of 12 years where the action started on or after this date. The period of possession for government land has to be 60 years.
As held in JA Pye (Oxford) Ltd v Graham  1 AC 419, for this action to be established, the possessor has to prove an actual possession or occupation of the property and the requisite intention to possess. Factual possession signifies an appropriate degree of physical and exclusive control that depends on the circumstances. The alleged possessor has been dealing with the land as an occupying owner might have been expected to deal with it. In this case, the paper owner was physically excluded from the land by the hedges and the lack of keys to the road gate. A similar circumstance occurred in Lambeth LBC v Blackburn  EWCA Civ 912, where the possessor changed the lock and exclusively controlled the property, indicating an actual possession.
The intention to possess is defined In Powell v McFarlane (1979) 38 P&CR 452 as an intention, on one’s own name and on one’s own behalf, to exclude the world at large, including the paper owner. Moreover, a trespasser needs not only to show his requisite intention to possess but to make such intention plain and clear to the world by actions or words. Usually, if the possessor occupied and made full use of the land in how the owner would, no additional evidence would be needed to establish the intention as his acts have already spoken his intention. Yet, the intention to possess would not be established if there was evidence pointing to a contrary conclusion or the acts claiming possession were equivocal and capable of more than one meaning. For example, in Tsang Foo Keung v Chu Jim Mi Jimmy  3 HKC 527, the possessors had been granted licenses in using the area, and this would preclude them from being seen as occupying the land as their own.
When a land or property owner discovers that someone else has been possessing his estate, he/she may originate summons following Order 113 of the Rules of the High Court. After obtaining the right of possession, the possessor can use and enjoy the land, while such a right is not equivalent to ownership.