Rival congresses of the Russian Communist Party are being held in Moscow on Saturday.
Leader Zyuganov had to read his speech by torchlight
Correspondents are forecasting an official split in the successor to the party which has dominated Russian politics for much of the last century.
On Thursday, opponents of party leader Gennady Zyuganov said they had voted him out of office and appointed Ivanovo region governor Vladimir Tikhonov.
But Mr Zyuganov refuses to stand down, saying most party members support him.
He has been under growing pressure to resign since the Communists suffered a heavy defeat by supporters of President Vladimir Putin in elections last December.
'War of attrition'
Mr Zyuganov opened his congress at a concert hall in eastern Moscow, while his rivals met at a secret location.
Both claim to have a quorum of registered delegates, and are expected to elect rival leaders, officially splitting the party.
It will then be up to the justice ministry to decide which of the parties is legitimate.
Correspondents say the pro-Zyuganov event seemed surreal, as lighting in the hall did not work and the leader was forced to read his opening speech by torchlight.
Mr Zyuganov admitted that the party was in crisis, but blamed the Kremlin for carrying out what he described as a war of attrition against it.
He denied that the party was split, and said his opponents had no support in the party.
The Communist Party remains Russia's main opposition, but with just 51 seats in the 450-seat parliament it can no longer seriously influence legislation.