PHNOM PENH, Sept. 21 (Xinhua) -- Cambodia on Sunday began to celebrate the three-day traditional Pchum Ben festival, or Ancestor's Day. In a special video message, Cambodian Prime Minister Hun Manet said Pchum Ben festival is a Cambodian tradition that has been observed annually since ancient times. Pchum Ben festival is the second-biggest celebration for Cambodian people after the Lunar New Year. During the holiday, hundreds of thousands of migrant workers leave the capital, Phnom Penh, for their hometowns in various provinces across the Southeast Asian country. "The free bus services aim to facilitate people's travel and help reduce travel costs for them," he said.