Rocks were thrown at vehicles on the Windang Bridge on Sunday, with reports of damage to at least three cars.
Lake Illawarra duty officer Inspector Steve Johnson said the first incident occurred about 9.50pm when a car was driving over the bridge on Shellharbour Rd, Windang.
"The driver heard a bang on the lower part of the front windscreen," he said.
"The windscreen was cracked and it appears a rock has been thrown at the vehicle."
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About 10pm, while police were still in the vicinity, a southbound vehicle was hit.
"The driver heard two loud bangs on his vehicle," Insp Johnson said.
Again the car was damaged, but no evidence of a rock or the perpetrators were found. No-one was injured in either attack.
A report of two more attacks over the weekend was posted by an online reader on the Illawarra Mercury website.
Identifying themselves only as "roundthemup", the reader said eggs were thrown at their car on Saturday about 10.30pm while driving on the bridge.
The reader also said that on Sunday afternoon, a Sydney driver's windscreen was smashed by a rock while driving over the bridge.
Insp Johnson issued a warning while appealing to the public for more information about the incidents.
"This is a very serious offence," he said. "The maximum penalty is five years' imprisonment."
Anyone with information about these incidents should contact Lake Illawarra police on 4295 2699 or Crime Stoppers on 1800 333 000.
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