RELATED PARTY TRANSACTIONS - MATERIAL BALANCES WITH GUANGZHOU RAILWAY GROUP AND ITS SUBSIDIARIES (Details) ¥ in Thousands, $ in Thousands	Dec. 31, 2021 CNY (¥)	Dec. 31, 2021 USD ($)	[1]	Dec. 31, 2020 CNY (¥)	Dec. 31, 2019 CNY (¥)	Dec. 31, 2018 CNY (¥)
Disclosure of material balances of related party transactions [Line Items]
Trade receivables	¥ 3,664,894			¥ 2,955,797
Provision for impairment of trade receivables	(23,751)			(60,704)	¥ (61,135)	¥ (61,212)
Prepayments and other receivables	171,059			242,601
Less: Provision for impairment	(6,503)			(10,590)	¥ (10,590)	¥ (10,590)
Trade and bill payables	3,112,710	$ 488,452		2,073,922
Contract liabilities	112,442	$ 17,645		215,305
Accruals and other payables	587,667			448,318
Guangzhou Railway Group and its subsidiaries [member]
Disclosure of material balances of related party transactions [Line Items]
Trade receivables	2,881,069			1,853,846
Provision for impairment of trade receivables	(16,028)			(24,099)
Trade Receivables From Related Parties Net	2,865,041			1,829,747
Prepayments and other receivables	83,808			59,580
Less: Provision for impairment	(62)			(51)
Prepayments And Other Receivables Due From Other Related Parties Net	83,746			59,529
Prepayments for fixed assets and construction-in-progress	7,270			0
Trade and bill payables	1,882,872			1,243,372
Payables for fixed assets and construction-in-progress	1,038,742			876,031
Contract liabilities	4,346			436
Accruals and other payables	495,930			443,754
Guangzhou Railway Group [member]
Disclosure of material balances of related party transactions [Line Items]
Trade receivables	600,042			208,024
Prepayments and other receivables	1,944			431
Trade and bill payables	71,414			67,889
Payables for fixed assets and construction-in-progress	334,313			111,799
Accruals and other payables	8,600			4,379
Subsidiaries of Guangzhou Railway Group [member]
Disclosure of material balances of related party transactions [Line Items]
Trade receivables	2,281,027			1,645,822
Prepayments and other receivables	81,790			59,070
Prepayments for fixed assets and construction-in-progress	7,270			0
Trade and bill payables	1,730,317			1,145,025
Payables for fixed assets and construction-in-progress	326,023			342,123
Contract liabilities	3,940			297
Accruals and other payables	468,064			426,821
Associates [member]
Disclosure of material balances of related party transactions [Line Items]
Trade receivables	0			0
Prepayments and other receivables	74			79
Prepayments for fixed assets and construction-in-progress	0			0
Trade and bill payables	81,141			30,458
Payables for fixed assets and construction-in-progress	378,406			422,109
Contract liabilities	406			139
Accruals and other payables	¥ 19,266			¥ 12,554

[1] Translation of amounts from Renminbi (“RMB”) into United States dollars (“US$”) for the convenience of the reader has been made at US$1.00=RMB6.3726, the certified exchange rates for December 30, 2021 as published by the Federal Reserve Board of the United States. No representation is made that the RMB amounts could have been, or could be, converted into US$ at that rate on December 30, 2021 or on any other date.