Updated

An out-of-control van careered across several lanes of traffic on a highway overpass Sunday, then plunged more than 50 feet off the side of the road and landed in a ravine on the grounds of the nation's largest city zoo, killing all seven people aboard, including three children, authorities said.

The van apparently flipped over a 4-foot-high iron fence before landing upside-down on the Bronx Zoo property. The cause of the crash was unclear, and police said they didn't yet know how fast the van was traveling. A city official said the guardrail's height would be one of the safety issues investigated.

The victims were three girls, ages 3, 5 and 10, an 84-year-old man and three women, ages 80, 45 and 39, police said. The 45-year-old woman was driving. The victims' names weren't immediately released.

The van was headed south on the highway that cuts through a working-class neighborhood when it bounced off the median, crossed all southbound lanes and hit the guardrail, police said.

The van landed in a wooded area on the edge of zoo property that's closed to the public and far from any animal exhibits, zoo spokeswoman Mary Dixon said. The vehicle lay mangled hours later, its right doors ripped off and strewn amid the trees along with items from the car. Next to the heavily wooded area are subway tracks and a train yard.

It's not clear what caused the van to go out of control. The southbound side of the highway was closed briefly Sunday afternoon while police investigated but later reopened.

The medical examiner's office said it expected to release the victims' causes of death on Monday.

The accident was the second in the past year where a car fell off the same stretch of the Bronx River Parkway. Last June, the driver of an SUV heading north lost control and the SUV hit a divider, bounced through two lanes of traffic and fell 20 feet over a guardrail, landing on a pickup truck in a parking lot. The two people in the SUV were injured.

City agencies will be asked to look at safety issues on the highway including guardrail height, Bronx borough President Ruben Diaz Jr. said in a statement Sunday.

"My prayers, as well as those of my office and all Bronxites, go out to the families of the seven victims," he said.

The wreck was the deadliest in New York City since the driver of a tour bus returning from a Connecticut casino in March 2011 lost control and slammed into a pole that sheared the bus nearly end to end, killing 14 passengers.

In 2009, just north of New York City in suburban Westchester County, a woman carrying a vanload of children drove nearly two miles in the wrong direction on a highway before colliding with an SUV. Eight people were killed, including four children. An autopsy determined that the woman, Diane Schuler, had downed at least 10 drinks and had smoked marijuana as recently as 15 minutes before the wreck.