Police on Monday said they had arrested six men in connection with the attacks in Yuen Long MTR station on Sunday night.
The force said they were being detained for illegal assembly.
It's understood that the men were seen wearing white T-shirts at the time of the violence.
Earlier the police chief Stephen Lo had defended the delay of more than half an hour before officers entered Yuen Long MTR Station to help victims of the attacks, saying some officers from the district were helping to deal with protesters on Hong Kong Island.
He added that at around the same time, the police were also called to three fights and a fire in the Yuen Long area and this had added to the delay.
Police said the first officers to arrive at Yuen Long MTR Station as a gang of men were attacking hundreds of people on Sunday night did not intervene immediately because they felt “their safety could not be guaranteed”.
The force has come in for serious criticism for what many say was a slow response to the attacks, with no officers in sight when men, mostly dressed in white and brandishing bamboo sticks, chased after and brutally beat MTR passengers and journalists.
Dozens of people required hospital treatment, with one critically injured and five others said to be seriously hurt.
The police commissioner was also asked about reports that people who phoned 999 were hung up on, or were told to stay home if they were scared.
The police chief was also pressed as to why people in Yuen Long who were seen wearing helmets and holding metal rods were neither searched nor arrested when police arrived.
Lo said he would learn more, and follow up.
Last updated: 2019-7-23 HKT 00:05
Police arrest six men over Yuen Long violence
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