Hundreds of thousands of people have joined May Day rallies across Asia, with protests sparking high alerts in the Philippines and Indonesia.
In the Philippine capital Manila police stopped thousands from reaching the presidential palace amid fears rallies would become anti-government protests.
In Indonesia, tens of thousands rallied against a planned labour law they say will undermine workers' rights.
Strong protest rallies were also held in Japan, Taiwan and Cambodia.
In Manila, 5,000 anti-riot officers were deployed amid fears of a repeat of the 2001 May Day riots, when government forces clashed with followers of ousted President Joseph Estrada.
[Arroyo] only has herself to blame for the rising tide of protests against her regime
Philippine protest leader
After rallies in Manila parks, about 7,000 activists and pro-Estrada supporters headed towards the presidential palace.
As they marched in a narrow street towards the historic Mendiola bridge - which has become a symbol of anti-government resistance - they were blocked by riot police.
However, there were no reports of serious violence and the rallies dispersed.
Many protesters were demanding the resignation of President Gloria Arroyo over allegations of corruption and vote-rigging.
Secretary general of the militant leftist group Bayan, Renato Reyes, said: "She only has herself to blame for the rising tide of protests against her regime."
In Indonesia's capital, Jakarta, protesters gathered in their thousands, waving trade union banners and demanding planned revisions to the 2003 labour law be dropped.
Leftist groups marched on the presidential palace in Manila
The protesters called President Susilo Bambang Yudhoyono an enemy of the worker.
About 13,000 security personnel, including riot police, were deployed in the city.
May Day is not a public holiday in Indonesia but many factories and businesses were closed.
Again there were no reports of violence in the country's rallies.
Opponents of the revisions to the labour law say they will curtail workers' freedom to organise and to strike, and will also reduce severance pay.
Supporters say they will make Indonesia more competitive.
Local media reports also spoke of large protests in the North Sumatran capital of Medan and in Makassar in South Sulawesi.
In Cambodia, there has been a huge police presence to enforce a ban on marches.
Cambodian labour head Chea Mony (R) is detained in Phnom Penh
Hundreds gathered in the capital Phnom Penh to defy the ban, but were stopped by police with riot shields and batons.
Police briefly detained Chea Mony, head of the largest labour organisation.
In Taipei, the capital of Taiwan, 200 workers marched in protest at their lay-off by a US firm.
Workers in Thailand marched to demand a 25% increase in the minimum wage.
In Japan, tens of thousands gathered in Tokyo to protest against the wealth gap between rich and poor and to call for better working conditions. http://news.bbc.co.uk/2/hi/asia-pacific/4961554.stm