Officers said a 52-year-old man was attacked by two men on Lai Wo Lane. He was later certified dead at the Prince of Wales Hospital.
Police raided a residential building in Mong Kok on Monday afternoon looking for the two assailants, but no arrests were made.
Speaking to reporters later in the day, superintendent Li Muk-yik said a 76-year-old man and his 47-year-old son were arrested on suspicion of conspiracy to commit murder.
Police said the pair planned the attack.
“Both of them have a triad background. Police believe that the victim had serious disputes with the two over money,” Li said.
Police are also looking for a suspected lookout at the scene, who is believed to have fled to the mainland.
His 28-year-old girlfriend was taken into custody for allegedly assisting offenders and misleading officers.
