A Belarusian Foreign Ministry spokesperson said the authorities viewed Romaszewska's journalism as "provocative and of an unfriendly character" but did not elaborate. The authorities did not tell Romaszewska why she had been detained.
"We deplore the deportation of Agnieszka Romaszewska, and demand that she be immediately allowed to return to Belarus and report freely," CPJ Executive Director Ann Cooper said.
Romaszewska had reported on a crisis in the city of Grodno in July over an ethnic Polish community center. Riot police took over the center and removed its leaders, according to international reports.
Polish-Belarusian relations have been tense in the past year. Polish authorities have criticized President Aleksandr Lukashenko for oppressing Belarus' 500,000 ethnic Polish minority. Lukashenko has accused Poland of plotting his downfall, The Associated Press said.
Romaszewska is the second Polish journalist deported recently. Adam Tuchinksi, a photojournalist with the weekly news magazine Przekroj was deported in August and banned from Belarus for five years. The same month, Belarusian authorities refused to admit independent Polish journalist Marcin Smialowski, who had press accreditation and a visa for the country.