Two plumes of smoke can be seen coming from different parts of the centre on the outskirts of Kidlington and there is a heavy police presence.
Initial reports suggested inmates had clambered on to the roof of the centre in Langdale Lane.
However latest eye witness accounts are that there is no-one up there now.
It is understood 15 fire engines have been called to Campsfield, which houses up to 200 male immigration detainees.
The police helicopter is also hovering above.
Paramedics have also been called in and what is thought to a detainee has been put into an ambulance.
A police spokesman would not comment on what had happened.
The centre has been the scene of several disturbances and protests by detainees about conditions.
Last July 26 inmates broke out.
It is run by private American firm GEO.
my 2c worth
if you park 15 fire engines there, there won't be room for much else