A top international cycling road race had to be cancelled after gale-force winds blew riders off course - and off their bikes.

Organisers of the annual Cape Town Cycle Tour decided to halt the event 21km into the 109km race.

They feared that competitors would be injured or even killed by the high winds or by debris being blown across the streets.

In a video compilation posted on In the Bunch, scores of riders can be seen battling the winds, which blew in excess of 100km per hour on parts of the route.

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Some riders were completely at the mercy of the gusts and were unable to do anything to stop themselves from ploughing into other competitors.

One racer laughed in disbelief as he held onto the handlebars of his bike as it was lifted up into the air, threatening to blow away.

But most of the competitors in the event, which is in its 40th year, looked worried by the dangers the weather posed.

In one clip a portable toilet hurtled across the course.

Spectators had to sit down to stop themselves from being blown off their feet.

Extreme winds also resulted in the cancellation of another South African road race, the 2017 Bestmed Tour of Good Hope, earlier this week.

In a statement, organisers said: 'Based on consultation with all the emergency services, the Joint Operations Centre of the Cape Town Cycle Tour 2017 regrets to announce that they have had to take the unprecedented step of cancelling this year's 40th Cycle Tour.

'This morning presented a number of challenges, not least of which were wind speeds considerably higher than predicted yesterday.

'This, combined with a large fire that broke out in Hout Bay in the early hours of this morning, and the added risk of protest action en route, were all contributing factors to the decision made in our Joint Operation Centre (JOC) by the VOC Commander to stop the event.'

Riders who had started the route were stopped at around the 21km point and escorted back by traffic authorities.

The organisers are arranging to donate all food and other resources that would have been given to riders during the event to those in need.

They said: 'We are in the process of co-ordinating efforts to ensure that goods reach those in need in the fire-affected areas in Hout Bay.'