Opposing colours, ideologies and songs were on display across Thailand's capital Friday as thousands of supporters turned out for the final rallies ahead of an election that is shaping up to be a generational clash.

Sunday's vote will be a tussle between establishment army-backed parties such as caretaker Prime Minister Prayut Chan-o-Cha's United Thai Nation (UTN) party and a resurgent opposition movement, fronted by Paetongtarn Shinawatra, daughter of polarising ex-premier Thaksin.

About 10,000 Pheu Thai supporters packed Bangkok's Impact arena -- normally the venue for rowdy K-pop and rock concerts -- creating an electric atmosphere as Paetongtarn returned to the campaign less than a fortnight after giving birth.

The stadium was a sea of red, the traditional colour of the political movement founded by Paetongtarn's father, billionaire Thaksin Shinawatra, in self-exile since being ousted as prime minister in a 2006 coup.

Pheu Thai's supporters were pumped up with an English-language rap song "Landslide" -- a reference to the party's call for a ringing victory to thwart any attempts by the army to keep them from power.

Pheu Thai has been ahead in polls, but their lead has narrowed with Pita Limjaroenrat, leader of the more radical Move Forward Party (MFP), edging ahead of Paetongtarn as people's first choice for prime minister.

MFP faithful streamed into the Thai-Japanese Stadium to hear Pita, 42, speak, many decked out in the party's orange, with tangerine-coloured ribbons in their hair.

"He will fight for the right thing," supporter Punjarat told AFP.

But there are dark clouds on the horizon for Pita, with rumours that MFP could face the same fate as its predecessor, the upstart Future Forward Party that performed well at the 2019 election but was dissolved by court order.

"I am worried, but we have to believe," said Nat, a 41-year-old government official, as he had a temporary tattoo of the MFP logo transferred to his face.

"I want Thailand to be changed for democracy, I want the country to be better."

The atmosphere inside the packed stadium was closer to that of a pop concert than a political rally, and organisers had to open up a football pitch next door to cope with the swelling numbers.

Behind the stage a heavily tattooed, pierced supporter with a bleach blond mohawk excitedly waved a giant flag as the crowd's mood built.

- 'No chaos' -

It was a different story next door at the ruling Palang Pracharath Party (PRPP) rally, where older crowds queued listlessly, with members handing out placards and inflatable tubes.

UTN and PRPP, both led by former army chiefs, have aimed squarely for older more conservative voters with a nationalist, royalist pitch warning of chaos if the opposition gets in power.

Attapong Chantaropas, 59, an odd-jobs man in Bangkok, said he was voting for the current ruling party to ensure stability.

"No chaos, no disruption, no conflict. Stop demonstrations or protests," he told AFP.

And at the UTN rally, instead of tattoos and rap music the crowd were stirred with a rendition of the royal anthem.

It was a sea of red, white and blue -- the colours of both the Thai flag and the UTN party -- as the crowd, many of them retirees, awaited Prayut's arrival.

"Prayut gets stuff done but doesn't boast about it. But he has a successful track record," said Kanokwan Choosai, 69.

"He cares about the elderly," added the retired food vendor, decked out in a ballerina costume with a red sash and feathers around her waist.