This story has been updated.

A dog followed children getting onto a school bus in Clinton Wednesday morning and then attacked and injured four people onboard, Prince George’s County police said.

Four students from Fort Washington Forest Elementary School were transported to Southern Maryland Hospital. Three of them have been released, according a school spokesman.

The incident occurred around 7:50 a.m., in the 12300 block of Winbrook Drive. Corp. Clinton Copeland, a Prince George’s Police spokesman, said the animal was apparently roaming free before it got onto the bus. A school spokesman said the bus driver fought off the dog inside the bus, preventing further injuries to students. That account came from parents who were dropping their children off and witnessed the attack, he said.

“Really, it was very heroic what he did by fighting that dog off,” Prince George’s County Schools spokesman Briant Coleman said.

Copeland said once the dog was off the bus, a police officer shot it. He said the officer "did attempt to restrain the dog," but the animal continued to act aggressively.

Copeland said it appeared the dog “did attack” the students, although the students did not seem to have provoked it. He said at least one student was bitten and had to receive stitches.

The school spokesman Coleman said one of the students was bitten and scratched and two others were just scratched by the dog. Those students, he said, had already left Southern Maryland Hospital. He said he was still seeking details on the fourth student injured, though he knew that the child had been taken elsewhere to seek medical attention.

The police said the dog was an American bulldog, although the school system’s press release said it was “believed to be a pit bull.”

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