The colloquial phrase long time no see, which first appeared in the USA in the 1890s, is used as a greeting meaning it is a long time since we last saw each other.

It originated in Chinese Pidgin English, after Chinese hǎojiǔ bú jiàn, or hǎojĭu méi jiàn, composed of:
– hǎojĭu, meaning long (time), literally good long (time),
– bù, or méi, meaning not, no,
– jiàn, meaning to see, meet.

The earliest instances that I have found are from a short story titled Lee Hing’s Girl, published in The Seattle Post-Intelligencer (Seattle, Washington) of 14^th February 1892; its anonymous author specifies on two occasions that the phrase originated in “pigeon English”, that is, Pidgin English:

Dawn was just breaking outside, and the smokers in Sam Sing’s Doyers street joint had reached that somnolent, semi-conscious condition which is the greatest fascination of opium smoking […].
“What time is it, Sing?”
The question came from a dark-haired young girl, one of a party of four who had
been smoking since the early evening. […] The girl was about 20 years old, of slight but superb figure, very pretty, with dark eyes and a mass of black hair that tumbled over her naked shoulders in rich profusion. The men were of a familiar class, handsome, well-groomed fellows, known to Inspector Byrne’s men as expert “handshakers.”
“Five minutes to 6,” answered the slick-looking Chinaman, as he appeared in the doorway.
“As late as that?” asked the girl in dreamy surprise. Then she aroused herself with an effort […].
“Well, I’m going. Good-by.”
“So long, Mame. See you tonight,” murmured the sleeping trio, who wouldn’t have disturbed themselves if Uncle Josh Hayseed, of Rubenville, had come to Doyers street shaking $I,000 at them to take a chance in their prize lottery.
“Good by, Mamie,” said Sing, as he unbolted the door for the girl. “You come back tonight?”
“Maybe. I think I go see my mamma today. Long time no see,” answered Mamie, who, from constant association, had, like the other girls of the neighborhood, fallen into the habit of talking pigeon English to the Chinamen. “Good by.”

She then asks ‘Chuck’ Connors, a prizefighter she knows, to go on an errand for her; first, they both go to the house where she lives with Lee Hing, but the latter threatens ‘Chuck’:

“Don’t you dare draw that knife. Lee Hing,” cried the girl, as she put herself between the two men. “I want send ‘Chuck’ my mamma; one letter; that all; no long time see,” said she conciliatingly, falling into the pigeon English.
“Goddam you,” returned the Chinaman, turning his wrath upon her. “Where you stay all night? You no think I know. You go Sing house smoke Melican loafer. What for you no stay here? You got pipe here. I cook you pill. What for you go way?”
“I go see one friend,” replied the girl. “Long time no see. He come Chicago. My brother he live Chicago. I go my friend at Sing house; like him talk my brother.”
“Goddam lie,” hissed Lee Hing. “No long time you see your mamma,” sneered
he; “no long time you see you flend; no long time you see you blother. All light: no long time you see me. I come back no more,” and he seized his hat and stalked out of the room.

The Oxford English Dictionary (3^rd edition, 2016) mistakenly speculates that long time no see was found “in early use in representations of North American Indian speech”, because the earliest quotation in this dictionary, from The Boston Daily Globe (Boston, Massachusetts) of 18^th February 1894, is:

Come to my tepee. Long time no see. Plenty game in mountains. We kill deer and bear.

[Likewise, the Oxford English Dictionary erroneously conjectures that the noun money tree is from Chinese qiánshù and that to shake the money tree is from the Chinese traditional phrase yáo qiánshù because the earliest quotations in this dictionary refer to China.]