Another official confirmed the crash to a local news outlet.
"The survivors said they saw one of the motors of the plane stop," Daniel Guedes, a police official in the city of Manacapuru near the crash site, told the Internet news portal Terra.
The plane - being used as an air taxi, a common practice in the thick jungle areas of Brazil - crashed into the Manacapuru river about 3:30 p.m. Saturday.
A cause for the crash was not yet known.
The state spokesman said rescue officials are on the scene and searching for other survivors, but so far just the four have been found.
Guedes told Terra the plane had left the city of Coari, 225 miles (360 kilometers) southwest of Manaus. The flight's destination was not immediately known.
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