The mayor was attacked at 0230 local time (0030 GMT) in the City Hall, which had opened its doors to the public as part of a series of all-night festivities.

He was completely conscious and determined that an isolated incident should not affect what was supposed to be a nice festival of Paris

Deputy Mayor Christophe Girard

The assailant - a 39-year-old man with a criminal record - was overpowered at the scene, and is now being questioned by police. The motive for the attack is unclear.

Officials said Mr Delanoe's life was not in danger, adding that he had undergone minor surgery at the nearby Pitie Salpetriere hospital.

Mr Delanoe, one of France's few openly gay politicians, brought the Socialists to power in the city last year and has been working to improve the quality of life in the city with cultural activities and projects to clean up the streets.

Sudden assault

The stabbing took place after Mr Delanoe had just returned to the opulent City Hall building from a tour of museums and other venues as part of the city's "Sleepless Night" celebrations.

Witnesses said the attacker approached Mr Delanoe as he was circulating freely among the crowd.

"The mayor was walking quietly in the Hotel de Ville's reception room when a man of around 40 threw himself on him without saying anything and stabbed him in the stomach with a knife," the mayor's aide Anne-Sylvie Schneider told the French news agency AFP.

Tourist attractions such as the Eiffel Tower were open all night

Deputy Mayor Christophe Girard said Mr Delanoe had insisted, before being taken to hospital, that the city's festivities should continue.

"He was completely conscious and determined that an isolated incident should not affect what was supposed to be a nice festival of Paris for the Parisians," he said

Dozens of tourist attractions, including the Eiffel Tower and the Louvre, were free of charge all night, and free concerts and exhibitions were being held around the French capital.

Series of attacks

Mr Delanoe, a softly-spoken and popular politician ended the rule of President Jacques Chirac's conservatives when he took office in early 2001.

Since then he has focused on carrying out his campaign pledge to improve the city's quality of life. Some of his initiatives have been hugely successful, including his "Paris Beach" project last summer.

Palm trees, parasols and sand were placed at the banks of the Seine River, creating a mock beach that drew thousands of sunbathers.

Mr Delanoe's 'Paris Beach' project was very popular with Parisians

But Mr Delanoe, who governs together with the environmentalist Greens, has also angered taxi drivers and small businessmen with his policies to cut down traffic congestion and pollution.

The attack was the second in less than three months against a prominent French politician.

On 14 July, a man tried to shoot President Jacques Chirac as he was reviewing troops at the annual Bastille Day military parade in Paris.

Earlier this year, eight local councillors were shot dead by a gunman in the western Paris suburb of Nanterre.