Passengers on a Jetstar flight bound for Tokyo have been forced to return to Brisbane following a medical emergency on board, before being left waiting on the tarmac for hours.

Flight JQ9 departed Brisbane Airport about 10.50am AEST on Friday but was diverted back after a passenger reportedly collapsed and lost consciousness.

Another passenger on board, who asked not to be named, told 7NEWS.com.au the emergency unfolded about 90 minutes into the flight, when cabin crew called for medical professionals to assist.

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“Over speakers they asked for medical staff like doctors or nurses. Someone has collapsed unconscious at the back of the plane,” she said.

The witness said crew rushed through the aisles carrying medical kits, while about 20 people gathered at the back of the aircraft.

She described feeling “unsafe” during the ordeal.

She said the aircraft dumped fuel for about 20 minutes before returning to Brisbane, where emergency services were waiting.

“When we landed, about five paramedics came on board and about five airport staff and border security,” she said.

“They put the person on a stretcher tarp thing and two staff members dragged the person out along the aisle.”

Staff also had to unload luggage to locate the affected passenger’s bag, the witness said.

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Disruption continues after landing

But the disruption continued after the aircraft landed, with passengers left waiting on board.

The witness said the plane had been sitting on the tarmac for about an hour as of 1.30pm AEST, with the pilot warning it would be at least another 45 minutes before departure.

She said she felt “unsafe” as the crew rushed through the aisles with medical kits.

She criticised Jetstar’s handling of the incident, saying the diversion had significantly disrupted travel plans.

“It has massively inconvenienced me and everyone else on board. Our travel will be delayed by at least 6 hours,” she said.

She said the delay could leave travellers struggling to find transport from Tokyo’s Narita Airport late at night, while some could lose a night’s accommodation.

She said Jetstar should provide some form of compensation for the disruption.

It is not yet known what caused the medical emergency or the condition of the affected passenger.

Jetstar responds to emergency

Jetstar confirmed a passenger experienced a medical episode on board the flight.

“The safety and wellbeing of our customers and crew is our number one priority,” a spokesperson for the airline said.

“We thank customers for their patience and understanding while our crew attended to a medical incident on board the flight.”

The airline said the flight was expected to depart Brisbane for Tokyo’s Narita Airport shortly.