Two men collapsed and died while taking part in Sunday's Bike for Mom cycling event to mark Her Majesty the Queen's 83rd birthday, one in Prachin Buri and the other in Nakhon Si Thammarat.
In Prachin Buri, Chalerm Prakorbkan, 83, fainted and suddenly toppled over while cycling with other participants along Suwanasorn road in front of Wat Chao Ngo in tambon Maikhet in Muang district.
He was given first-aid treatment at the scene and then rushed to Chakrapong Military Hospital, where he was pronounced dead.
Chitra Promsuthima, the Prachin Buri governor, and Maj Gen Prawit Chayabut, commander of the 12th Army Circle, were among the people who later turned up at the hospital and expressed condolences to his family.
Chalerm's daughter Tassanee Prakorbkan said her father had a strong desire to take part in the event because he also turned 83 this year, the same age as Her Majesty the Queen.
A funeral for Chalerm is being held at Wat Kochasarnmuneesi (Nong Khe) in Muang district of Prachin Buri.
In Nakhon Si Thammarat, Ratchapol Rungkamchad, 46, a Highway Department engineer attached to the Nakhon Si Thammarat Highway Office 1, also fainted and fell from his bicycle at Vajiravudh Camp in front of the 15th Infantry Battalion while taking part in Bike for Mom.
He was admitted to Vajiravudh Military Hospital, where he was pronounced dead from a concussion to the head.
Ratchapol had been part of the group that started in front of the city hall, intending to complete the full 33-kilometre distance.
His medical record showed he suffered from a heart ailment.
His body will today be moved to Wat Na Phra Borommathat for funeral services. Governor Peerasak Hinmuangkao was to lead the bathing rite on Monday afternoon.
Three people were injured while taking part in the cycling event in the northern province of Phayao.
Thienchai Passornyothin, 63, a retired education inspector, and his 30-year-old wife Mrs Or both fell when their bikes became entangled. Mr Thienchai broke his right arm while his wife sustained a minor injury.
The third person was Long Thamthong, 63, who took part riding a tricycle. He suddenly fell unconscious during the ride.
All three were rushed to the provincial hospital and later proclaimed to be in no danger.