A total of 607,909 people signed up to take part in the "Bike for Dad" cycling event during the nine-day registration period, organisers said on Wednesday.

The cycling celebration scheduled for Dec 11 is planned to mark His Majesty the King's 88th birthday, which is on Dec 5.  

A total of 498,105 people registered in the provinces, 99,999 in Bangkok and another 9,805 from overseas.

Nakhon Ratchasima has the highest number of registered bikers outside the capital, with 29,766, followed by Sakon Nakhon (17,865), Kanchanaburi (14,113), Songkhla (12,684) and Si Sa Ket (12,348).

Interior permanent secretary Krisda Boonraj said cyclists turned out in large numbers nationwide to sign up on Tuesday, the last day for registration.

Sources said the cabinet on Tuesday discussed whether Dec 11 should be declared an official holiday.

However, the meeting agreed that it was not necessary to do so as there are already many holidays in December. Instead, cooperation may be sought from the various agencies to allow their staff to participate.

Prime Minister Prayut Chan-o-cha voiced concern over safety on that day with a large number of people taking part in the event potentially causing heavy traffic congestion. Dec 11 is a Friday.

He asked all agencies involved to ensure all activities are carried out smoothly.