A man crosses a street in smoggy conditions in New Delhi, India. Millions of people in India's capital started the week choking through "eye-burning" smog, with schools closed, cars taken off the road and construction halted. Photo: AFP

The start of a leading Asian Tour golf tournament was held up Thursday by toxic smog that has engulfed the Indian capital with hazardous levels of pollution.

Organizers of the four-day Panasonic Open India event said the tournament could be shortened if the pollution remains serious, as completing the event would be "a big challenge."

Delhi and other cities across northern India are blanketed by a poisonous haze each winter due to build-up of traffic fumes, industrial emissions and smoke from agricultural fires.

"The opening round of the Panasonic Open India was delayed due to poor visibility and weather conditions," an Asian Tour organizer told AFP.

The first golfers went on the course five hours late and some wore anti-pollution masks.

A photo posted on Twitter by the Asian Tour showed Bangladeshi golfer Mohammad Siddikur Rahman hitting a shot while wearing a face mask.

The amount of PM2.5 - deadly tiny particles that get into the bloodstream and lungs - soared to about 20 times the safe limit set by the World Health Organization.

Delhi authorities closed all schools until Friday, banned construction and are only allowing cars on the road depending on whether the registration is an odd or even number.

The road rationing is meant to end on Friday, but Delhi chief minister Arvind Kejriwal said it could be extended.