Two cyclists have been airlifted to hospital after separate crashes on the 100-mile RideLondon event. Thousands of keen cyclists have taken part in the annual event on Sunday 31 July which takes riders from east London through the city and Westminster to Surrey and back.

South East Coast Ambulance Service has said that one man is in a serious condition after hitting a tree whilst cycling and another man is being treated for a serious head injury after falling off his bicycle.

The first crash is said to have taken place around 9.05am near Pyrford, Surrey, with riders being held up on the pre-established route before being diverted another way. The man was taken by air ambulance to St George's Hospital in Tooting, London, where he remains under medical supervision.

Almost two hours later, at around 10.55am near Thames Ditton a suburban village in south west London, a second crash took place with air ambulance paramedics taking the injured man to a London hospital.

Organisers of the popular event tweeted: "Due to an incident that required an air ambulance to attend, riders in the RideLondon-Surrey 100 have been held on the route in Surrey. Planned contingency route from West Byfleet to Ripley is being opened & riders will be directed to that route. More info when available."

Some participants and spectators on social media said that they were waiting in the same position for upwards of 45 minutes. Dominic Harris, who is taking part in the event, said on microblogging site Twitter: "RideLondon participants waiting patiently in Pyrford following what is understood to be a medical incident ahead."

Another Twitter user Maria David said: "Been stuck at Pyrford feed station about 45 minutes. Apparently air ambulance on the road up ahead."

Shortly before noon, RideLondon tweeted: "The route from West Byfleet to Ripley has been now been re-opened to riders in the Prudential RideLondon-Surrey 100. The diversion route is no longer in use."