HONG KONG — As the protests in Hong Kong have gotten more violent, a bloodier summer of unrest, more than half a century ago, has loomed ever larger.

In 1967, a labor dispute at a plastic flower factory led to a series of protests and lethal riots in Hong Kong, which was then a British colony. By the time it was over, more than 50 people were dead.

No one has been killed this summer in clashes between demonstrators and police officers or brawls between civilians, like the ones that broke out on Sunday night in and around the city’s North Point neighborhood.

But Hong Kong officials are haunted by the possibility, and Sunday’s bare-knuckled brawls ended in a haze of flashing ambulance lights. At least 28 people were injured in clashes in North Point and other neighborhoods throughout the day, including a 49-year-old man who the local media said was beaten unconscious by a mob of protesters.