As many as 86 cars and trucks collided on Interstate 95 east of Baltimore yesterday in a series of crashes that occurred along a 10-mile stretch during a sudden, blinding storm.

At least 18 people were taken to hospitals after as many as 11 crashes in Baltimore and Harford counties occurred starting about 4:30 p.m., authorities said. Many collisions involved several vehicles.

At least four people, apparently the most seriously injured, were taken by helicopter to Maryland Shock Trauma Center in Baltimore after the crashes, one of which involved as many as 20 vehicles. Their conditions were not immediately known, but one official said it appeared none of the injuries was life-threatening.

I-95, the major north-south traffic artery on the East Coast, was shut in both directions for hours.

More than four hours after the accident, all southbound lanes, where most of the crashes occurred, remained closed. According to accounts from authorities and witnesses, only the shoulder of the northbound lanes had been opened in some spots as efforts continued to clear away debris.

The collisions occurred northeast of Interstate 695, the Baltimore Beltway, and southwest of the Susquehanna River Bridge. At least four crashes occurred in the highway's southbound lanes and at least one in the northbound lanes.

In the most visually compelling of the crashes, a tractor-trailer stopped atop a car, apparently crushing part of it. But none of those involved in that crash appeared to be among the most seriously injured, said Daniel F. McMullen, acting executive secretary of the Maryland Transportation Authority.

He said the most severe injuries apparently were suffered by the occupants of a single passenger car.

The causes of all the collisions were under investigation last night. Authorities said the weather appeared to be a prime factor.

"There was a severe line of thunderstorms with hail, high winds and heavy downpours," McMullen said.

When visibility suddenly is impaired in such conditions, he said, "people seem to pile on before they realize what happened." Sometimes "you come upon these things quickly," he said.

McMullen did not know how quickly the flow of traffic was traveling when the crashes occurred, but he said: "It's a highway where people move very, very expeditiously."

Initial accounts indicated that the accidents were "rear-enders," said Maj. Greg Shipley, a spokesman for the Maryland State Police. The accidents came about because "people couldn't see."

The crashes occurred between White Marsh in Baltimore County and Route 543 in Harford County. The Harford sheriffs office said it was told that the White Marsh crash involved 21 vehicles.

"Any time you shut down I-95, it is an incredible event," said Robert L. Flanagan, secretary of the Maryland Department of Transportation, citing the high volume of traffic on the highway.

Authorities said many motorists were diverted onto nearby U.S. 40, "which clearly is not equipped to carry that volume of traffic," Flanagan said. Route 7 also was used to divert traffic.

A motorist traveling north on I-95 shortly after the crashes said rescue and cleanup personnel swarmed the area. Some were involved with cleaning up fuel spills from damaged vehicles, said the motorist, Karen Cavanaugh.

Of the collision that ended with the tractor-trailer atop the car, Cavanaugh said, "that was the biggest." She said that she saw at least 20 damaged cars but that they "didn't look as bad."

A spokeswoman for Maryland Shock Trauma Center said that four patients had been received and that one more was believed to be on the way.

Last year, about 80 vehicles collided in Western Maryland in three crashes. In 2001, 114 vehicles piled up on I-95 near Quantico in what authorities said might have been the largest crash on the Eastern Seaboard.

Rescue personnel tend to the collision that involved as many as 86 vehicles east of Baltimore on Interstate 95. A sudden storm is likely to blame.