Hanoi motorbike taxi drivers turn first aiders

On the tarmac of a dark Hanoi street, motorbike taxi driver Pham Quoc Viet mops the bloodied knee of a fellow rider, one of the hundreds of traffic victims he's tended to in the chaotically congested Vietnamese capital.

By day, Viet, 33, works for Southeast Asian ride-hailing firm Grab, scooting along the tree-lined boulevards and winding alleys of the city.

But from 9.30 pm until 1.30 am, he is an unofficial emergency responder, a red flashing light secured to his handlebars as he patrols the streets on two wheels.