(Revises number of farms, adds details)

WARSAW, Dec 1 (Reuters) - Two poultry farms north-west of Warsaw were cordoned off after the deadly H5N1 strain of bird flu was found in turkeys, Polish officials said on Saturday.

Earlier reports had said three farms were affected, but the governor of Mazowsze province, where the outbreak occurred, later revised the count.

"A third farm had initially been suspected but that suspicion was not confirmed," Governor Jacek Kozlowski told a news conference in Plock.

There are plans to cull 4,000 birds at farms around the village of Brudzen near the city of Plock, Poland's chief veterinary officer Ewa Lech said on television.

She said the virus was most likely brought to Poland by migrating ducks, geese or swans, adding that an area within a 3-km (1.8 miles) radius of the outbreak had been cordoned off.

"Areas of contamination and danger have been marked off and are being constantly monitored by veterinary officials and police," said Plock crisis-management official Hilary Januszczyk.

The virus has caused more than 200 deaths in humans globally since 2003, according to World Health Organisation data.

Most people who have caught bird flu have had direct or indirect contact with infected fowl but experts fear the constantly mutating virus could change into a form easily transmitted from person to person.

Poland's efforts to contain the spread of the virus won the approval of the European Commission.

"The Polish authorities notified us in the middle of the night about a strong suspicion of bird flu," European Commission spokeswoman Barbara Helfferich told Reuters.

"We have been in contact with them since then, they are now taking the appropriate measures."

This includes disinfection mats over which pedestrians and vehicles entering and leaving the affected areas must pass, Polish officials said.

Bird flu was discovered in wild swans near the north Poland city of Torun in early 2006.

"There is no cause for alarm," Polish Prime Minister Donald Tusk said on television.

"I am in touch with the interior and health ministers as well as veterinary officials in charge. This is not the kind of threat we had several years ago." (Reporting by Marynia Kruk and Rob Strybel; Editing by Stephen Weeks)