* Chinese soybean buyers resell around eight cargoes
* Resales come after huge imports in recent months
* Import surge causes logjam, 17 vessels anchored in Rizhao
BEIJING/SINGAPORE, Aug 7 (Reuters) - Two major Chinese soybean buyers have resold more than 500,000 tonnes of product in recent weeks, sources familiar with the deals said, amid growing concerns about losses among crushers and congestion at a major port in the world's top oilseed buyer.
The resales appear to be isolated, but they stir worries about possible contract defaults as crushers incur big losses due to a supply glut and a logjam in the port of Rizhao, China's major crushing hub in eastern Shandong province.
Three years ago, during a similar period of high stocks and loss-making margins, contract defaults swept the market and traders dumped hundreds of millions of dollars of beans back onto the market to avoid losses. (http://reut.rs/2uhdgZh)
In the recent resales, Shandong Sunrise Group, a major importer, flipped four to five cargoes back to the market, said three China-based traders and one Singapore-based trader familiar with the issue. The sources all declined to be identified as they are not authorised to speak to the press.
Rapidly expanding crusher Shandong Sanwei Oil & Fat Group has also resold three cargoes, said two of the traders.
Eight cargoes would be equal to 520,000 tonnes of soybeans, worth around $210 million, based on June customs data.
Sunrise and Sanwei, however, resold the cargoes at much below market rates, said the Singapore-based trader, who works for a global trading company that has oilseed processing plants in China.
The identity and location of the buyers are not known, and staff in the international trading departments of Sunrise and Sanwei declined to comment.
The resales may have been triggered by a tightening of credit, said the four traders. Cargoes are sometimes shipped before the buyer has received a letter of credit (LCs).
"Some importers are facing credit issues and have been unable to get LCs," said the Singapore-based trader.
It was not clear if Chinese banks were tightening credit for the sector or if it is part of a wider clampdown on lending across the economy. Beijing has pledged to curb some types of financing after a rapid build-up in debt last year.
The trend will fuel worries that China's demand for more bean imports may fall. Preliminary import data will be released on Tuesday.
Shipping data from Thomson Reuters Eikon shows 17 dry-bulk carriers anchored off Rizhao port waiting to deliver their cargo. Traders said most of them were carrying soybeans.
Adelante <C 3/4BO7309524118> has been waiting unable to berth and discharge cargoes since late May, while Great Victory <C 3/4BT7309776084> has been moored there since middle July, as huge arrivals overwhelmed facilities.
The two vessels are carrying an estimated 130,000 tonnes of beans, worth about $45 million based on Monday's prices.
Crushers in Shandong have been losing money per tonne crushed <JCI-SBMG-SHDNI> since late February, swinging to a profit for only four days in the first half of July before returning to the red.
They are currently losing 83 yuan on each tonne of soybeans processed, with margins pressured by soymeal stocks <CFD-SBMST-NATN> that are at their highest on data going back six years.
(Reporting by Dominique Patton in BEIJING and Naveen Thukral in SINGAPORE; Additional reporting by Beijing newsroom; Editing by Josephine Mason and Tom Hogue)