BEIJING (Reuters) - A Chinese agriculture group has warned that export policies for phosphate may tighten due to rocketing domestic prices, urging companies to curb speculative buying and stabilise supplies.

China is the world's biggest exporter of phosphate and a major producer of urea, but it stepped up export restrictions late last year, including longer inspection times at ports and asking producers to prioritise domestic supplies.

Concerns over unreliable Chinese supplies have prompted Asian fertiliser buyers to turn to producers in Russia, Vietnam, Egypt and the Middle East.

The China Agricultural Means of Production Association (CAMPA) said fertiliser producers and distributors should be wary that rising phosphate prices may lead to a further tightening of export policies.

As of July 15, the average wholesale price index of domestic di-ammonium phosphate (DAP) and mono-ammonium phosphate (MAP) have risen by 9.99% and 23.08% from a year ago due to higher costs of raw materials and weak seasonal demand, CAMPA said in a statement late on Tuesday.

Companies should "fulfill their social responsibility, and actively respond to the national policy requirements of maintaining supply and price stability to ensure that the domestic supply of fertilizers is sufficient", it said.

China's exports of phosphates have already slowed this year.

Shipments of DAP during January-May slumped 30.6% from a year ago to 1.03 million metric tons, while MAP exports dropped 30% to 61,000 metric tons, Chinese customs data showed.

Urea exports have plunged 91.7% from a year ago to 70,000 metric tons.

(Reporting by Mei Mei Chu; Editing by Kim Coghill)