BEIJING, May 19 (RIA Novosti) - Chinese authorities have imposed quarantine restrictions in a county in the northwest Qinghai Province amid fears of a possible bird flu outbreak, Xinhua said on Tuesday.

Sanitary authorities began culling poultry and disinfecting farms after the deadly H5N1 virus was discovered in 121 dead migratory birds in the Gonghe County.

No cases of human H5N1 infection have been registered so far.

As of May 15, a total of 424 human bird flu cases, resulting in 261 deaths, had been registered worldwide since the virus was first detected in 2003, according to the World Health Organization statistics.

With 38 official bird flu cases and 25 deaths, China remains the fourth hardest-hit country after Indonesia, Vietnam and Egypt.