The tanks took positions at around 4:15 pm at the entrance to the airport, where French and African peacekeepers are based, after automatic weapons fire and explosions shook several parts of the city, an AFP journalist reported.
Tens of thousands of people have taken refuge on the airport grounds since sectarian bloodletting erupted early this month in the former French colony, claiming hundreds of lives.
The heavy machine gun fire was apparently not directed at the airport but was especially intense in the nearby PK12 area.
Peacekeeping troops were also absent from the streets, with only one helicopter, probably French, circling above.
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Earlier today, a spokesman for the African peacekeeping force MISCA said its Chadian troops would be redeployed out of the capital amid charges they were siding with a former rebel group.
"The whole Chadian contingent will be sent to secure the north in the next few days," MISCA spokesman Lieutenant Colonel Ndong Toutoune told AFP.
The Chadians, mainly because they are Muslim, face accusations by many in Bangui of complicity with the mostly Muslim Seleka rebels who overthrew president Francois Bozize in March in the predominantly Christian country.
Amnesty International says some 1,000 people have been killed since December 5, mostly by Muslim ex-rebels but also in Christian reprisal attacks.
The head of the Burundian contingent in the African MISCA force told AFP his men were disarming former rebels on Monday when Chadian troops from MISCA threw a grenade and opened fire on them, prompting some Burundian elements to return fire, wounding three Chadians.