Dozens were wounded in Thai capital Bangkok when a grenade was hurled at anti-government demonstrators marching through the city at midday.

Protest leader Suthep Thaugsuban was in the procession near Chulalongkorn University in the city centre but was not wounded when the explosive device was thrown into a lorry driven by demonstrators.

The city's emergency services centre put the number of injured at 31.

Police said the grenade was hurled from a nearby building.

Anti-government demonstrators seeking to oust Prime Minister Yingluck Shinawatra have taken over seven key roads and overpasses in Bangkok this week, blocking them off with sandbag walls and steel barricades.

The protests, which are also aimed at derailing February 2 elections, have been generally peaceful.

But acts of violence have been reported nightly, including shootings at protest venues and the hurling of small explosives at the homes of top protest supporters. It is unclear who is behind them.

Even small-scale violence increases the risk of a military coup, which would benefit the protest movement.

The army has seized power 11 times since the end of absolute monarchy in 1932.

Overnight, two motorcycle riders drove past the residence of Bangkok Governor Sukhumbhand Paribatra and threw a grenade inside.

Mr Sukhumbhand, who is member of the Democrat Party which is backing the protesters, was not home and no injuries or serious damage were reported.

The attack was similar to another grenade attack on the home of former Democrat prime minister Abhisit Vejjajiva.