The protestors gathered at the Ram Lila grounds near New Delhi's main commercial area for the protest organised by the Jamiat Ulama-i-Hind, a Muslim religious organisation.

Police put the number of protestors at around 50,000 but organisers claimed some 300,000 people had turned up.

A smaller protest was held at the historic 17th century Jama Masjid mosque in Old Delhi, witnesses said.

"We do not want Bush here as he is the world's biggest terrorist. He has no place in the land of (freedom hero Mahatma) Gandhi," said Jamiat Ulama-i-Hind spokesman Abdul Hameed Naumani.

The protestors shouted "Bush murdabad" (Bush die) and "Bush vaapas jao" (Bush, go back), amid demands to ban the Danish newspaper which printed controversial cartoons of the Prophet Mohammed last year.

Addressing the rally, Communist Party of India general secretary A.B. Bardhan called the US president an "imperialist aggressor" for his invasion of Iraq and for "bullying" Iran over its nuclear programme.

Left-wing parties and workers' organisations were preparing for similar protests on Thursday.

Eight political parties, most of them communist, have formed a Committee Against Bush Visit, which will hold a "people's march" and put up cartoons and T-shirts poking fun at Bush on Thursday.

"President Bush is the topmost official of US imperialism, leading enemy of the sovereignty of nations and the peoples of the world today," the committee said in a statement Wednesday.

The left-affiliated cultural organisation Sahmat said activists from other outfits had made cartoons, posters and T-shirts for the protests bearing slogans such as "Killer in town".

Hundreds of students at Jawaharlal Nehru University were joined by Booker prize-winning writer Arundhati Roy late Tuesday in keeping a night vigil against the visit.

Muslims are enraged over US foreign policy in the Middle East. Left-wing parties also opposed to its economic policies, which they say exploit the poor.

The communists are scathing in their criticism of the Indian government for its softening stance towards the US, which they say is interfering in Indian foreign policy.

With around 130 million Muslims among its 1.1 billion inhabitants, India has one of the world's largest Muslim populations.

Meanwhile Delhi authorities have thrown a security blanket never seen for any head of state, with anti-Bush protestors pledging to take to the streets in thousands against the US President during his visit here March 1-3.

In an unprecedented act, Delhi Police have asked motorists to avoid several arterial roads in the heart of the city Thursday when George W Bush will have a packed day in the national capital.

Also Thursday 50,000 to 100,000 people are expected to march from the Ramlila ground to Parliament Street, armed with posters, banners and Bush caricatures.

"We are protesting against everything Bush stands for," said Rajan, one of the organisers of Thursday's rally that will draw more than 100 small and big groups ranging from mainstream political parties to fringe outfits.

The office of Sahmat, a Left-leaning cultural body, is overflowing with a variety of anti-Bush stickers and posters and even T-shirts that mock at the US president, who is visiting India for the first time.

After initial hesitation, the police have finally relented and allowed the demonstrators to go up to Parliament Street, normally the venue of protests but a spot the authorities earlier did not want the anti-Bush rally to reach.

Delhi Police have told people working in thousands of offices located in and around downtown Connaught Place to positively make it to their work places by 9.30 a.m. Thursday, after which many roads will be sealed off for hours.

Even students appearing for their Class 10 and school-leaving examinations Thursday have been told to reach their respective centres in these areas by 8.30 a.m., almost two hours before the exams start.

"We appeal to the parents to make sure that their children reach the centres in north and central Delhi early. These areas would be under strict security as Bush goes from his hotel to Mahatma Gandhi's memorial," said Qamar Ahmad, joint commissioner of police (traffic).

"We know it will cause problems to students but arrangements have to be done for VIP movement," Ahmad said

Around the time Bush holds talks with Prime Minister Manmohan Singh at the stately Hyderabad House, thousands will gather at the Ramlila ground not very far away to kickstart a protest rally that is expected to take three hours to reach Parliament Street, less than a kilometre from Parliament House.

Both colourful and black-and-white posters denouncing Bush have sprouted on walls in many places.

Leaders of the Communist Party of India-Marxist (CPI-M), which supports the government but is opposed to Bush's visit, have assured the government that the protest would be peaceful.

The police, however, are taking no chances.

The mainstream political parties are not their worry but fringe groups are, outfits that might want to make an anti-Bush point violently. Among those ranged against the Bush visit is the Communist Party of India-Maoist, which believes in violence as a creed.

The US has brought in a mind-boggling array of security gear, including three helicopters, anti-aircraft guns, radio jammers and armoured limousines for the security of Bush. The airspace over Delhi will be sealed when Bush arrives and departs.

Tens of thousands of police and paramilitary personnel will be on duty during Bush's stay.