Ten people have been injured in four separate multi-vehicle crashes across a "hectic" three hours for emergency services in Sydney.
The latest collision was between a number of vehicles, including two trucks, at the intersection of the M7 and M2 motorways in Seven Hills just before 10am on Tuesday.
A 47-year-old male truck driver, understood to have abdominal injuries, was taken to Westmead Hospital in a stable condition, CareFlight says.
The second truck driver was also taken to the same hospital with minor injuries.
"There were other vehicles reportedly involved in the collision but no other passengers known to have serious injuries," CareFlight said in a statement.
Earlier, a man was trapped in a wreckage in southwest Sydney for almost an hour, suffering a leg injury, after two trucks and two other vehicles collided about 7am on the M7 at Prestons.
All southbound lanes have reopened, with traffic queues of up to 16km easing, according to the Transport Management Centre.
Half an hour later, two women also became trapped inside an ambulance van after it collided with a garbage truck and a car in Frenchs Forest.
The pair have been taken to hospital for medical checks, while the garbage truck driver was treated at the scene for chest and neck injuries. The car driver was uninjured.
"It was very hectic at the scene," a NSW Police spokeswoman told AAP on Wednesday.
Emergency services were called out to a collision involving at least five cars less than an hour later on the Princes Highway in Waterfall, with paramedics treating four people at the scene for minor injuries.
Police say one vehicle had veered off into the bush and another four cars were across the centre median strip.
NSW Police has issued a reminder to motorists that "school zones are back in action" this week.