Amid tight security, some state legislators voted to remove Peter Obi for gross misconduct on Thursday.

His deputy is refusing to be sworn and civil rights groups have criticised the whole process as unconstitutional.

A BBC correspondent says the battle could get more volatile if supporters of the two sides take to the streets.

Election battle

Mr Obi, who has been in office for just seven months, only took power after a court ruled that his predecessor had rigged the election in 2003.

This is the fifth state to start impeachment proceedings against a governor this year.

Some say the recent impeachments are part of the fight against corruption.

But critics say it is often more about rival politicians trying to take charge of the state so they can control the elections due early next year.

Mr Obi, from the opposition All Progressives Grand Alliance (APGA), has only occupied the post since March this year.

That was after an appeal court rule that the elections in the state in 2003 were rigged by the governing People's Democratic Party.

The PDP's Chris Ngige, who occupied the post of governor illegally for three years, had fallen out with senior party figures soon after the election.

He said it was because he refused to loot public money to pay them back for their support.

Since Mr Obi took office in March, he has been locked in a power struggle with one of the president's closest aides, Andy Uba, who wants to win the governorship in next year's elections.

Analysts say the impeachment process could only help this ambition.