A festive scene quickly turned to horror Saturday night after a vehicle said to be traveling nearly 70 mph crashed into a crowded church street fair, injuring 35 people, authorities said.

A 7-year-old in the car was unhurt, but two children under 3 were among dozens sent to the hospital. Seven people were severely injured, including two police officers who drove their motor scooters in front of the car to try to stop it.

Witnesses reported seeing the driver smoking something as she barreled through several blocks and hundreds of people. Strollers were sent flying through the air and a person was seen pinned under the car's wheels after it bowled into a stage of dancing revelers at the annual Unifest fair in Anacostia.

"We're still trying to piece together exactly just what happened that led up to this," District of Columbia Police Chief Cathy L. Lanier said at the scene.

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Tonya Bell, 30, of Oxon Hill, Md., was taken into custody near the scene and charged with aggravated assault while armed. Lanier said additional charges are pending.

"The armed part of it, of course, being the vehicle,” said Rod Wheeler, a former D.C. homicide detective.

“They need to charge her right away to hold her. … More charges are going to be coming down this week.”

Wheeler said police likely are investigating two theories.

“She had some kind of medical problem” and became unable to operate the vehicle or, “She was high, probably off of a drug known as PCP,” Wheeler told FOX News. “That drug on the street is known as ‘dippers,’” he said, adding that it is a marijuana cigarette dipped in embalming fluid and also is known as “wacky tobacky.”

“You just basically lose your mind,” he said.

Authorities were conducting blood tests to determine if alcohol or drugs were involved.

A half-hour before the festival crash, a car reportedly driven by Bell was seen driving erratically, striking a police car and fleeing the scene of that incident, Lanier said.

Alan Etter, a spokesman for the District of Columbia fire department, said authorities believe Bell was going about 70 mph when she tore through the festival. Litter and debris from food stands were scattered in the street. Some of the victims reportedly suffered head injuries and major blood loss.

Witnesses described an extended period of mayhem in which the driver started off slowly through some closed streets and finally hit the accelerator on the avenue running through the heart of Unifest, an annual event sponsored by a church. The car hit a stage where people were dancing, witnesses said. It was not clear what finally caused it to stop.

Ryland Anderson, 19, and Philemon Walker, 24, told The Washington Post they were about to cross the street as the festival was winding down when the car sped past. They described strollers being flung into the air and said they saw the body of a man apparently lodged in the station wagon's wheel well.

"She was driving like 'if you're in my way, you're going to get hit,"' Walker said.

David White, president of the Chicago Shannon Civic Association, said Bell grew up in the neighborhood and is well known. White said he and other residents saw her in the area on Saturday morning, driving erratically and clipping parked cars. He said he confronted her, but she acted like she didn't know him.

"I said, 'Tonya, what are you doing?' She was sweating like a race horse. We tried our best to stop her. ... She was just in a deranged state of mind," White said.

Unifest, which was celebrating its 25th anniversary, is Washington, D.C.'s premiere African-American cultural festival and parade and draws thousands each year.

It was founded by Union Temple Baptist Church in 1982 as the "Chitlin Strut, Chicken Stroll, Down Home Cultural Festival and Parade" and highlights the culture, diversity and rich history of African-Americans and the Anacostia neighborhood of Washington in a spirited two-day celebration.

The Associated Press contributed to this report.