The attack happened when the pair boarded the bus on West Tamaki Rd, near the intersection with St Heliers Bay Rd, Acting Detective Senior Sergeant Anthony Darvill said.
"A group of young males and females have made demands for property towards the two victims," he said.
"Both victims were assaulted, one of which sustained bruising to her face."
Darvill said police found and spoke to a group of young people, and they were making further inquiries.
It follows an attack on a bus in East Auckland in June which left a 16-year-old student with severe facial injuries.
Police later arrested a 39-year-old woman and described the attack as a "hate-motivated crime".
Last month, RNZ reported on data from Auckland Transport (AT) showing the number of assaults against drivers in the first six months of 2024 rose to 33 up from 21 over the corresponding period a year earlier.
AT said it was aware of the latest attack and the bus operator had provided footage to the police.
"We were sorry to hear about this horrible incident. The safety of everyone who uses our transport network and facilities is our top priority and thankfully, incidents of this nature are still rare across the busy transport network that sees over 1.6 million trips each week," a spokesperson said.
This month AT brought on an extra nine transport officers patrolling buses, trains and ferries.
"Transport officers are vital to ensuring safety on buses, trains and ferries, and the new recruits are really enjoying positive interactions out on the transport network," AT said.
"They are warranted to give out tickets for fare evasion, but they are also there to help keep everyone safe and are well trained to do this."
The spokesperson said AT continued to collaborate with operators and unions on measures to improve safety.
"Anti-social behaviour is a societal issue, so we do require everyone's help - whether it's police, community groups or members of the public who can report anything they see."
AT said its buses are fitted with CCTV, GPS and panic buttons that record sound, connecting directly with the bus depot.
It also planned to install driver screens to 80 percent of its buses over the next two years.
