The action triggered widespread concern about media freedom in Turkey, with critics accusing the government of trying to silence opponents of Erdogan's Justice and Development Party (AKP) before Sunday's legislative vote.
Police in riot helmets moved in after a controversial court ruling ordered the seizure of companies held by the Kozi-Ipek conglomerate linked to US-exiled preacher Fethullah Gulen, a one-time Erdogan ally now regarded as his arch- nemesis.
Brawls erupted outside the offices, prompting police to use tear gas and batons against demonstrators, including lawmakers from the main opposition Republican People's Party (CHP).
Several arrests were made, media reports said, but crowds remained outside the building, which also houses the Millet and Bugun newspapers, around noon.
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CHP lawmakers and Bugun TV editor-in-chief Tarik Toros were seen negotiating with police chiefs who tried in vain to cut the live broadcast.
"This is an operation to silence all dissident voices that the ruling party does not like, including media outlets, opposition parties and businessmen," Toros said.
Sunday's election is crucial for the AKP, which lost its parliamentary majority in a June vote, scuppering Erdogan's hopes of changing the constitution to expand his presidential powers.
"Today is a shameful day... Everyone who made this decision and those who implemented it will have to answer for their crimes," said CHP lawmaker Baris Yarkadas.
The United States also voiced concern about media freedom in its NATO ally.
"We continue to urge Turkish authorities to ensure their actions uphold universal democratic values... Including due process, freedom of expression and assembly, and of course access to media and information," State Department spokesman John Kirby said.