General Constantino Chiwenga warned of military intervention to back independence figures after President Robert Mugabe purged his prominent second-in-command.
Morgan Tsvangirai and Evan Mawarire were among those to address a protest march.
The African country is suffering a crippling cash shortage.
The Zimbabwean opposition leader on how an economic crisis is leading to change.
Protesters using the national flag could face up to one year in prison.
Thousands of Morgan Tsvangirai's supporters marched through Harare on Thursday.