(TMZ) -- Meek Mill's supporters filled the streets of Philadelphia to demand his release from prison ... as Rick Ross and Dr. J provided some inspiration.

The #FreeMeekMill campaign got several hundred people marching Monday evening, with his label honcho, Rick, right in the middle of action.

NBA Hall of Famer, Dr. J made a speech to the crowd, but was nearly drowned out by "Free Meek" chants. In addition to the rally, an online petition pushing for Meek's release now has over 350,000 signatures.

The Philly rapper started serving a two to four year prison sentence last week for violating his probation.

#rickross out in #philly showing #meekmill support

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