A small town in central Thailand prepared for a sombre mass funeral on Thursday for the 23 children and teachers who died in a horrific bus fire while on a school trip.

Some residents and monks waited past midnight at Wat Khao Phraya Sangkharam, the Buddhist temple in Lan Sak town in Uthai Thani province, to receive the bodies of the dead returned from Bangkok.

Also arriving back were relatives of the dead who went to the Thai capital to help identify the severely burned victims.

The school the children attended is on the temple grounds, a common location for schools in much of rural Thailand.

In the school’s assembly hall, florists came early to build a large display of white flowers in front of a line of coffins with portraits of the dead.

An elderly woman wept in front of a photo of a 14-year-old boy before limping away, tears streaming down her face and and hands tightly clutching a black plastic bag. Relatives put food, snacks and beverages as offerings on top of the coffins — an act of respect symbolically sending nourishment and blessings to those who died.

The afternoon funeral was to be attended by the head of Thailand’s Privy Council as a representative of the royal family. King Maha Vajiralongkorn has declared a royal cremation ceremony will be held for the victims next week.

Six teachers and 39 elementary and junior high school students were on the bus that caught fire on Tuesday on a highway in suburban Bangkok. It spread so quickly, only 22 were able to escape.

On social media, parents have expressed nervousness about sending children on school field trips as well as deep outrage about potential safety lapses.

Police were investigating whether the fire was caused by negligence and filed several initial charges against the driver, including reckless driving and failing to stop to help others.

Police have not determined the cause but say the driver told them a front tire malfunctioned and the vehicle then scraped a concrete highway barrier. The sparks from the friction might have set off highly flammable gas canisters on the bus, police said.

The bus had 11 gas canisters inside, but a permit to install only six. Many Thai vehicles use compressed natural gas for fuel.

The bus company owner had told public broadcaster ThaiPBS the gas cylinders had passed safety standards.

Thailand’s Department of Land Transport was implementing urgent inspections of all natural gas-fuelled buses.

The department also will upgrade its safety guidelines to require crisis management training for drivers and safety inspection when such vehicles are to be commissioned by schools, said Seksom Akraphand, the agency’s deputy director-general.