Here are the latest developments in the story:
Chief Minister Nitish Kumar is meeting senior leaders from his party, the Janata Dal United or JD(U). They are likely to adopt a resolution which ends their 17-year-partnership with the BJP.
The resolution is expected to target Narendra Modi, the Chief Minister of Gujarat, without naming him. Mr Kumar wants this resolution to serve as a credible compendium for his decision, one that will appeal to voters.
Before formally announcing the split, the chief minister is expected to meet Bihar Governor DY Patil this afternoon to brief him of the developments.
Earlier today, the 11 BJP ministers in the Bihar cabinet skipped an emergency meet called by the Chief Minister. Instead, they met with their leader and Deputy Chief Minister Sushil Kumar Modi.
The BJP ministers are likely to give their resignations to Mr Modi, who will hand them over to Nitish Kumar.
"What is the point in a cabinet meet now? Nitish Kumar should clarify his plans for alliance," Bihar BJP President Mangal Pandey said.
The BJP's decision to place Narendra Modi in charge of its election campaign has precipitated the crisis. The JDU says he "lacks secular credentials."
If the JDU quits the alliance, its president Sharad Yadav is expected to quit as Convenor of the National Democratic Alliance or NDA. The BJP anchors the national coalition of nine parties; the JDU is its biggest partner.
The BJP in Bihar says that the state voted for the alliance, not the JDU alone, and Mr Kumar is, therefore, obliged to resign as chief minister and face an election.
To prove his majority in the state assembly, Mr Kumar needs 122 votes. The JDU has 118 state legislators.
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