A 71-year-old woman was sent flying from her seat after a Wellington bus driver suddenly braked while heading down the Ngauranga Gorge this morning.

An ambulance had to be called for the injured woman, who was thrown on to the floor by the abrupt motion, a witness said.

Nigel Sloley was on the number 1 bus from Churton Park as it made its way down the gorge just after 8am.

"All of a sudden there was a surge in speed and then a massive braking, which flew everybody forward. This unfortunate lady ended up from her seat, flashing, landing on the floor," he said.

The woman was "quite shaken and in shock" after the incident, and stayed on the floor for some time while the driver and other passengers tried to calm her.

Sloley heard the woman say she was 71, and that she was from Levin.

The bus driver told Sloley he was okay to continue driving, despite looking particularly shaken himself.

"I must admit, I was glad to get off the bus at the end," he said.

"I would have thought they would have at least sent another driver to take over and at least give the guy a break to gather his own thoughts."

Sloley said it was another thing in the "never ending saga" of the Wellington bus network.

While it did not have anything to do with scheduling issues, it was just another negative incident.

"It's just every day there seems to be something else with the buses. It's just a continuing saga, this one's now resulted in an incident. Had there been more people standing . . . anything would have been possible."

A Greater Wellington Regional Council spokesman referred questions on the incident to police.