A deadly military clash along Thailand and Cambodia's shared border is escalating, with airstrikes carried out by the Thai army.

Both sides have accused each other of firing the first shot as border tensions between the two South East Asian neighbours heat up.

Armed clashes on the remote, disputed border between Cambodia and Thailand have killed at least 12 people on Thursday, in a dramatic escalation of tensions that threatens to erupt into a broader conflict.

Thailand and Cambodia traded accusations Saturday of fresh attacks as deadly border clashes entered a third day, leaving at least 33 people dead and more than 168,000 displaced, as international pressure mounted on both sides to reach a ceasefire.

Thailand and Cambodia exchanged heavy artillery fire for a second day on Friday as their worst fighting in over a decade intensified and spread to new areas.