A small plane headed to the jungle city of Manaus crashed Saturday in Brazil's Amazon with at least 20 people on board, and at least 16 were missing and feared dead, officials said.

Four people survived, and local media reported that divers had found six bodies by nightfall.

The plane was being used as an "air taxi" to ferry passengers between cities in the thick jungle when it crashed in the Manacapuru river about 50 miles southwest of Manaus, the capital of Amazonas state, a state government spokesman said.

Authorities said 20 people were on board, but some Brazilian media outlets put the number at 24.

Rescuers found four people who escaped without major injuries from the plane, said the spokesman, who spoke on condition of anonymity in line with department policy.

Divers discovered the bodies of six people inside the submerged plane and believed they would find more when they search again, fire department Lt. Col. Dinanci Almeida told the UOL Noticias news Web site.

Survivors told authorities they saw one of the plane's motors stop, Daniel Guedes, a police official in the city of Manacapuru near the crash site, told the Internet news portal Terra.

Guedes told Terra the plane had left the city of Coari, 225 miles southwest of Manaus. The flight's destination was Manaus.

Calls to Guedes office Saturday evening rang unanswered.

A spokeswoman for Brazil's Civil Aeronautics Agency — known as ANAC — in Brasilia gave the plane's tail numbers as PT-SEA. According to ANAC's Web site, the plane with that tail number is an Embraer EMB-110P1 model, a small twin turbo-prop plane that carries up to 21 people.

Brazil's Center for Investigation and Prevention of Flight Accidents, or Cenipa, said the pilot had tried to turn the plane around near the site of the crash.

"The plane lost radio contact near the city of Manacapuru, but had indicated that it was turning around and returning to Coari," said a Cenipa spokeswoman who didn't give her name per department policy. "The pilot gave no reason for the action."

The spokeswoman said the area where the crash occurred had seen rainy conditions throughout the day, but could not confirm what the weather was like when the plane went down.

O Globo newspaper, citing Brazilian aviation officials, said the pilot reported to air controllers in Manaus shortly before the crash that the plane had encountered driving rain.

A cause for the crash was not yet known and it was not clear if any tourists were on board.

The Folha de S. Paulo newspaper, citing an unnmamed local police official, said the plane was packed with members of one family heading to Manaus to celebrate a relative's birthday.