More than 300 participants gathered Wednesday for a national forum sponsored by the International Finance Corporation.
Cambodia saw two senior-level visits from both countries week, including a stopover Monday by US Secretary of State Hillary Clinton.
Air France suspended service to Cambodia more than 35 years ago, with the country on the verge of collapse to the Khmer Rouge.
In 2002, China announced an undisclosed debt cancellation estimated at the time to be between $60 million and $1 billion.
Cambodia, one of the poorest nations in the world, typically needed aid from both sides to supplement its annual budget and to develop.
China is also a significant investor in Cambodia in garments, textiles, hydropower, agriculture and mining.
Decades of conflict shattered Cambodia's infrastructure - its roads, ports and railways.
More than 100 police cleared out vendor stalls surrounding the Olympic Stadium in Phnom Penh on Friday.