Capt. Syafii Nafsikin said search and rescue teams rushed to the scene.
Survivors, swimming to shore, were screaming in panic.
The sprawling, 770-yard (700-meter) bridge — built to resemble the Golden Gate Bridge in San Francisco — linked the towns of Tenggarong and Samarinda in East Kalimantan province.
It was clogged with traffic when the accident occurred, Syaiful, a witness, told local television station TVOne.
He saw at least one bus and close to a dozen motorcycles plunge into the Mahakam river. Several cars were mangled.
“Everyone was screaming,” said Syaiful who, like many Indonesians, uses only one name.
East Kalimantan police spokesman Col. Antonius Wisnu Sutirta said it wasn’t immediately clear why the 10-year-old bridge collapsed.
He said at least three people were killed and 17 others were injured and rushed to nearby hospitals.
