Seven people have been wounded, one critically, after gunmen on motorcycles opened fire on anti-government protesters in Bangkok, Thailand.

The gunmen opened fire on protesters in central Bangkok at around 2am, and at least one other attack took place nearby, police said.

"Unidentified assailants opened fire in the early hours of this morning ... at an intersection near the Khao San Road tourist area. Altogether seven people were injured, most of them anti-government protesters," said national police chief Adul Saengsingkaew.

The attack came just hours after clashes between government supporters and protesters outside Bangkok that left at least six people hurt.

The incidents occurred as authorities draw up plans to deploy more than 14,000 troops and police on Bangkok's streets from Monday.

From then protesters led by former opposition politician Suthep Thaugsuban aim to paralyse the city for between 15 and 20 days.

The turmoil is the latest episode in an eight-year conflict that pits Bangkok's middle class and royalist establishment against the mostly poorer, rural supporters of Prime Minister Yingluck Shinawatra and her brother, former premier Thaksin Shinawatra, who was overthrown in a military coup in 2006.

Eight people, including two officers, have been killed and scores injured in violence between protesters, police and government supporters in recent weeks.