The truck slid into the opposite lane leading to collisions with four other vehicles in the crash that occurred shortly after 8pm at Pratteln, cantonal police said.
The driver of the Italian truck was seriously injured, while a woman driving a car in the opposite direction suffered minor injuries, police said.
The truck, travelling toward Pratteln, crashed through the median of the six-lane highway 400 metres after a rest stop for reasons not explained, police said.
The truck driver and the woman motorist were both taken to hospital.
Debris from the crash was scattered over a 100-metre area and 14 tonnes of olive oil spilled onto the road making for “extremely slippery conditions,” police said.
Officials estimated damage in the hundreds of thousands of francs.
Police said there was no threat to the environment from the spill.
Salvage and cleaning operations were expected to continue until at least 5am Wednesday, blocking the highway.
A total of 100 workers were involved in the mop-up operation.
Traffic was diverted to an alternate route.
The accident occurred three days after a bus carrying members of the Marcus Miller Band jazz group overturned on the same highway, killing the driver.
Eleven members of the band, including MIller, a Grammy-Award winning bassist, were injured, along with another driver.