Cambodia saw two senior-level visits from both countries week, including a stopover Monday by US Secretary of State Hillary Clinton.
In 2010, China has invested $610 million.
In 2002, China announced an undisclosed debt cancellation estimated at the time to be between $60 million and $1 billion.
Last week, the leader of a demonstration for housing rights was severely beaten by police, as UN Secretary-General Ban Ki-moon toured.
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.
Prime Minister Hun Sen told UN Secretary-General Ban Ki-moon he wanted the office head in Cambodia to be sacked.