Encounters with apparitions have reportedly taken place within a number of situational contexts. The one which most people tend to readily think of is the context of a haunting, in which the ghostly figure of a deceased person is seen in a certain place where that person had once lived or worked in life. But in many instances, apparitions have also been encountered in the context of a crisis situation, in which a witness sees the spectral figure of someone who is ill, has been in an accident, is facing a life-threatening scenario, or has even just died. Many early "crisis apparition" encounters of this type were described in the various cases of psychic experience collected by the early members of the Society for Psychical Research (SPR) and published by Edmund Gurney, Frederic Myers, and Frank Podmore in their classic two-volume anthology Phantasms of the Living in 1886. Among these was Case #241, which presents a personal account given by Mr. S. J. Masters, describing an apparitional encounter that he'd apparently had around Easter time:
Last Easter Sunday, I was retiring to bed, just after 11 o'clock, and had stepped off the stairs on the landing that led to my room (my parents' bedroom door being in front of me, about 10 or 12 ft., and my door being about 2 ft. to the right, so that I had to pass it to get to my room). I saw their bedroom door was open, and I was rivetted to the spot by seeing standing in the room doorway in front of me, a figure of a female; although I could not distinguish the dress, I could plainly see the features, and especially the eyes. I must have stood there at least 20 seconds, for my mother, hearing me stop suddenly before reaching my room, at last opened the door (below) and asked what was the matter. I then came downstairs and stopped [i.e., stayed] with them till we all retired together. The figure collapsed when my mother called upstairs, and the light I held in my hand shone through the doorway to the opposite wall, which had been obscured by the figure, as if it had had a tangible body.
It was not till the following Wednesday that my mother, on reading the mid-weekly local paper, saw the death of a young lady with whom I had once kept company for a short time. On inquiry, I found she died about the same time as I saw the apparition. I feel convinced it was her, for the eyes had the same expression, although I could not recognise her at the time; not having seen the girl for quite six months, I had almost forgotten her existence. She died in decline, which accounts for her not being about the town before her death. [1, Vol. II, pp. 59 - 60]
Corroboration of Mr. Masters' account came from his mother, who recalled the occasion on which the encounter occurred and how it had affected her son. Through a records search, it was possible to trace the young lady's death to the approximate time period that Mr. Masters recalled having his encounter (although there were some slight discrepancies regarding the exact day, which might've been due to minor errors in Mr. Masters' own memory of the encounter). Though not as frequently as they were back then, crisis apparition cases like this one are still occasionally reported in the present time [2; 3, Ch. 7], with one of the most recent being reported in the pages of the SPR's own journal in January of 2014. 
This case is also notable for what it seems to tell us about a particular characteristic of apparitions: Largely through cultural stereotypes based in folklore, apparitions have often been thought of as being wispy, translucent figures that float or glide around. In direct contrast to this, Mr. Masters' account suggests that the spectral figure he saw looked solid, as implied by how it had apparently obscured the light (from the candle in his hand) from reaching the far wall while it was visible. This is consistent with surveys that have been conducted of other reported cases of apparitional encounters, which have found that seeing opaque or solid-looking figures is actually more common than one might initially think.
For instance, in his classic 1953 survey of cases, British psychical researcher G. N. M. Tyrrell noted that apparitions,
...when at their best, they are...indistinguishable from material figures normally perceived, so far as visual and auditory senses are concerned. [5, Apparitions, p. 58].
In their own survey of cases, British researchers Celia Green and Charles McCreery similarly noted that:
The majority of visual apparitions are opaque rather than transparent, the figure of the apparition seeming to blot out the part of the real environment behind it, as a real person would. Ninety-one percent of our subjects who reported visual experiences said that the apparition they saw was completely opaque like a normal object so that nothing was visible through it, rather than at all transparent so that they could see what was behind it. [6, p. 150]
Icelandic researcher Erlendur Haraldsson also found that reports of solid-looking figures made up a considerable part of his survey:
Almost three quarters of our informants said the deceased person had been physically present until he or she disappeared (73 percent), which could be understood to mean that they felt as if the person was there in the flesh. In 15 percent of the accounts the deceased person was only perceived to be physically present in part, that is, they were transparent, or only a part of the person could be seen. [3, p. 121]
Thus, while wispy and translucent apparitions are sometimes reported on occasion, it would seem that a good number of them are said to look solid, even to the point where witnesses may initially mistake them for being a real person. Such a thing apparently occurred in the classic "Morton Ghost" case, in which the spectral figure of a woman in black that seen in the home of the Despard family was thought to be a real woman at first by some witnesses who saw her.  This would appear to be one instance in which an aspect of apparitional folklore does not measure up well with encounters in real life.
The PRF would like to wish everyone a peaceful and joyous Easter holiday!
 Gurney, E., Myers, F. W. H., & Podmore, F. (1886). Phantasms of the Living [2 vols.]. London: Trubner & Company, Inc.
 Stevenson, I. (1995). Six modern apparitional experiences. Journal of Scientific Exploration, 9, 351 - 366.
 Haraldsson, E. (2012). The Departed Among the Living: An Investigative Study of Afterlife Encounters. Guildford, UK: White Crow Books.
 Murdie, A., & Fraser, J. (2014). Case note: The spontaneous hallucination of a recognised person coincident with death. Journal of the Society for Psychical Research, 78, 39 - 43.
 Tyrrell, G. N. M. (1953/1961). Science and Psychical Phenomena/Apparitions. New Hyde Park, NY: University Books.
 Green, C., & McCreery, C. (1975). Apparitions. London: Hamish Hamilton, Ltd.
 Morton, R. C. (1892). Record of a haunted house. Proceedings of the Society for Psychical Research, 8, 311 - 332.