Officials did not immediately confirm the report that Gamal Mubarak has fled to the British capital with his wife and daughter aboard a private jet.
The jet with Mubarak, his family and 97 pieces of luggage on board left for London on Tuesday from an airport in western Cairo, according to the US-based Akhbar al-Arab.
Weeks of unrest in Tunisia eventually toppled president Zine al-Abidine Ben Ali earlier this month. The anti-government protests in Egypt broke out after opposition groups waged an internet campaign inspired by the Tunisian uprising.
An anti-riot police officer was killed in clashes on Tuesday in central Cairo, Egyptian daily 'al-Wafd' reported. Egyptian security forces reported used tear gas, fire hoses, and clubs to disperse protesters in Tahrir Square, downtown Cairo.
Over 30,000 anti-government protesters had gathered. in Cairo's Maidan al-Tahrir square to take part in the 'day of anger', the spokesman for Egypt's '6 April' opposition movement, Mohammed Adel, told Adnkronos International (AKI) in an interview.
"Police used tear gas and water canon to break up our protest and they arrested 40 of us, but we don't have official figures on the numbers of arrests across Egypt," said Adel.
Supporters of the '6 April' movement, the opposition al-Ghad party, the outlawed Muslim Brotherhood, the al-Wafd party and supporters of former UN nuclear watchdog chief Mohammed El Baradei took part in the protest.
The protesters want Egypt to end its 30-year state of emergency and pass a law preventing a president from serving more than two terms, and want the interior minister Habib al-Adly, to resign.
Al-Wafd daily said police arrested 600 people during Tuesday's protests in Cairo, Alexandria, Port Said, Tantan, al-Mahala, Asiut, al-Bahira and al-Quium.
Between 200,000 and 300,000 people took part in protests in these cities on Tuesday, according to the Rasad al-Ikhbari observatory, which is staffed by journalists and opposition activists.
Police set dogs on protesters in Port Said and charged protesters in Suez and al-Mahala, an unnamed activist from Rasad al-Ikhbari told AKI.
Protests are rare in Egypt, where Mubarak tolerates little dissent.
US secretary of state Hillary Clinton said on Tuesday Washington believed the Egyptian government was stable and urged restraint on both sides.