Two children were reportedly killed in Thailand this morning when rockets fired by Cambodia hit a petrol station.

Bandit Aunjit, age seven, and Namkhong Boontang, aged eight, were reportedly killed when an artillery attack hit a 7-Eleven store at a PTT petrol station in Si Sa Ket province on July 24.

Officials said up to eight people believed to have been killed along with several injured in explosions nearby.

Locals in the Kantharalak district said they heard gunfire from both sides starting at 9am, which continued for more than two hours.

Soldiers evacuated residents from high-risk areas, causing long traffic jams - the worst escalation in the border conflict between the two countries in decades.

The Royal Thai Army reported that Thai military officers at Prasat Ta Muen in Surin, Thailand, heard the sound of an unmanned aerial vehicle at 7.35 am but could not pinpoint its location.

Six armed Cambodian soldiers, including one with an RPG, then approached the barbed wire area in front of the Thai base, prompting Thai soldiers to shout at them to stop.

At 8.20 am, the Cambodian side reportedly fired in the opposite direction of the base to the east of the castle before artillery fire was launched around 9 am.

Jirayu Huangsap, spokesman for the Prime Minister's Office, said the government received military information and clear evidence that the Cambodian side initiated the attack.

Cambodian PM Hun Manet said Thailand initiated the attack this morning, forcing him to retaliate. Troops reportedly fired continuous artillery rounds using 122mm rockets from BM-21 rocket launchers at residents in Surin.

One civilian was killed, while a five-year-old child was severely injured along with two family members, and seven soldiers were also harmed.

The Army closed all border checkpoints at 8 am, while the Ministry of Foreign Affairs was instructed to prepare evidence of the situation and provocation over the past seven months for submission to international organisations.

The Royal Thai Embassy in Phnom Penh advised Thai residents in Cambodia to leave as soon as possible.

The embassy also requested cooperation in avoiding non-essential travel to Cambodia until the situation is resolved.

Cambodian Ministry of National Defence officials released a statement condemning Thailand for encroachment.

Prime Minister Hun Manet said Cambodia 'had no choice' but to respond with its armed forces against 'armed aggression'.