About 11,000 tonnes went to the United States in 2008, which was by far the biggest export market for greenshell mussels.
New Zealand Greenshell, which farms in the Coromandel, will supply Oriental Ocean, with Opotiki's Eastern Seafarms coming on board once its production is established.
New Zealand Greenshell managing director Peter Vitasovich said the 20,000-tonne figure was far from concrete, but a first shipment to Oriental Oceans was expected once the new mussel season began in October.
A group of firms - Aotearoa Seafood, New Zealand Greenshell, Pacifica Seafood and Sanford - have also set up an office in China to market under the name New Zealand Pure Greenshell Mussels.
Opotiki's Eastern Seafarms, which will drop 5km of its first mussel lines next month, reportedly has a target of $250 million turnover within 15 years and is expected to create 900 jobs in the impoverished district.
The 3800ha farm has been set up as a joint venture between Opotiki's iwi, Whakatohea, and Sealord.
The district's aquaculture will eventually expand into fin fish, scallops and oysters.
Opotiki's delegation also negotiated with Oriental Ocean to receive expertise and direct cash investment for a sea cucumber farm.
Ponds will be dug onshore to harvest what is an expensive delicacy in China, with the first commercial trials on 2ha to begin within six months.
The New Zealand sea cucumber is regarded as virtually indistinguishable from the species harvested in China for medicinal properties.
Eastern Seafarms director Ian Craig said the district had built up an almost exclusive relationship with the Chinese giant over years of meetings.
Opotiki Mayor John Forbes said the town's relationship with Oriental Ocean was a special one and would serve it well into the future.
"In China, you don't walk in and drop a business proposal on the table. You do a lot of relationship building, and if they decide you're appropriate, then later on you can start to discuss proposals," he said.
"They've taken quite a shine to our Maori leadership and hold them in high esteem."