At least five attackers fired at the vehicle on a highway in Yala, one of the three provinces hit by a three-year separatist struggle, as it tried to escape an ambush, Colonel Acra Tiproch, an army spokesman, said.
Four men, two women, a boy and a girl were each hit by several bullets, a Reuters reporter said.
There are almost daily bombings and shooting attacks targeting representatives of the Thai authorities - police, soldiers, teachers and sometimes ordinary civilians.
Officials blame Muslim insurgents for much of the unrest, although criminal gangs are also thought to be behind some of the attacks.
Wednesday's ambush took place a day after the anniversary of the founding of the Barisan Revolusi Nasional (BRN), one of the main separatist groups in the region.
The minibus was headed for Hat Yai, the commercial capital of the predominantly Muslim south, from Betong on the Malaysian border.
Australia has issued two travel alerts for Thailand in the past few weeks, saying intelligence pointed to a high threat of bombs attacks and security forces are on full alert in the capital, Bangkok.
Already this week, a Myanmar migrant worker has been beheaded, several schools - often targeted as a symbol of the Bangkok government - have been burned down and a bomb was set off at a morning market.
A string of co-ordinated blasts across Yala, Narathiwat and Pattani provinces last month killed nine people and injured 44.
The south was an independent sultanate until it was annexed by overwhelmingly Buddhist Thailand a century ago.
More than 2,000 people have been killed in the region since the latest separatist violence started in January 2004.
|The bus was shot at in a "red zone" where security forces have previously been attacked [AFP]|
Police had warned that insurgents might try to mark the anniversary by launching attacks in the area.
Already this week, a Burmese migrant worker has been beheaded, several schools have been torched and a bomb set off in a morning market.