WARSAW (Reuters) - A fourth centre of the H5N1 bird fluvirus has been found in central Poland, about 50 km (30 miles)from three sites found last week, chief veterinary officer EwaLech said on Saturday.

The emergency services, following a standard procedure, setup a safety perimeter around the sites.

"The problem is the farm on which the virus was found is abig one, tens of thousands of birds," Lech told Reuters.

The latest cases of the virus were the first of bird fluamongst poultry as opposed to wild birds reported earlier.

Poland's agriculture ministry scheduled a press conferenceon Sunday at 4:00 p.m. EST.

(Reporting by Patryk Wasilewski)