Heroic efforts by tug boat operators and ship pilots averted major damage to Sydney's commercial port on Tuesday night, after the super storm that hit the city snapped the mooring lines of a 67,000-tonne container vessel, causing it to collide with another ship and shear the mooring lines of a third vessel.

Hapag-Lloyd vessel the Kiel Express broke free from its mooring in Port Botany as winds reached 126km/h – or category 2 cyclonic strength – just before 9.30pm, causing a trail of destruction.

"I've been in the maritime industry for close to 30 years and I've never seen anything like this," Jason Sellars, a chief engineer on one of six tug boats called out for the emergency, said. The operation lasted some nine hours.

"The only thing we were missing was George Clooney and it was The Perfect Storm," Mr Sellars said, referring to a popular Hollywood disaster film.

The ship cut the mooring of the OOCL Hong Kong, sending it free. The stern of the Kiel Express then collided with a stationary Safmarine vessel, the Makutu. The Kiel Express then swung around to collide side by side.

At one point, one of the tugs, operated by PB Towage, was at risk of being caught between the Kiel Express and the 62,000-tonne Makutu. Another tug boat became disabled when its propellers snagged on a mooring line cut loose on the Hong Kong vessel.

That ship had to be anchored away from the docks but could not be taken further out to sea because its containers had not been fully secured after its unloading operations were halted before the storm.

It's understood that the OOCL Hong Kong is undergoing repairs after its stern was punctured by the bollards on the wharf as the vessel swung out after its mooring was cut.

Philip Holliday, the chief operating officer of the Port Authority of NSW, said shipping operators had been warned to put out additional mooring to secure their vessels ahead of the storm.

"Whatever people did, it wasn't enough," Mr Holliday said, adding he was "quite relieved" the mishap ended without any injury and no environmental damage.

While investigations continue, the ships appear to have suffered only superficial damage, while two cranes that had been hit would be able to resume operations. The port was due to reopen late on Wednesday night.

"All the cheese holes aligned [on Tuesday night] to make this a bad storm," Mr Holliday said. "It could have been a lot worse."

DP World, which operated the dock where the vessels were moored, said it would undertake a "full investigation".

"Right now we are concentrating on returning to full operation," Nicole Holyer, the operator's national communications manager, said.

"The precise details we don't want to get into because the investigations are in the hands of the insurers," Ms Holyer said. "Most importantly, no one was hurt in the incident or the storm."

The Australian Maritime Safety Authority is also conducting an investigation to ensure the vessels are seaworthy, a spokeswoman said.