Britain has called on Egyptian President Hosni Mubarak to "listen urgently" to protesters as pressure for him to quit intensified.
Foreign Secretary William Hague delivered the message after tens of thousands of demonstrators again defied a government curfew to remain on the streets.
More than 50 people are now said to have been killed and thousands injured in five days of clashes between police and crowds demanding economic, social and democratic reform.
Efforts by Mr Mubarak to contain the crisis and prolong his three-decade reign appeared to be having little success. On Saturday evening he appointed former intelligence chief Omar Suleiman as his new deputy, having dismissed his whole cabinet overnight.
But the army seems unwilling to intervene to quell the uprising, and the US and UK - long-standing allies of the president - have refused to back his regime. America is reviewing its multibillion-dollar aid package for Egypt in light of the violence.
Nobel Peace Prize winner Mohamed ElBaradei, a leading opponent of Mr Mubarak, has returned to the country to join the dissidents but is believed to have been put under house arrest.
The Foreign Office has advised Britons against "all but essential" travel to Cairo, Alexandria, Luxor and Suez, while extra diplomatic staff have been flown out to help those stranded. An estimated 30,000 UK nationals are in the country, but the majority are in the relatively safe Red Sea resorts.
Mr Hague said of Mr Mubarak: "We call on him now to listen urgently to the aspirations expressed by the Egyptian people. He must seize this moment to make these reforms real and visible and to base them on the universal values that are the right of people in all countries. Peaceful reform, not repression, must be the way forward."
Mr Hague said travel advice for Britons is under "constant review", adding: "I am sending additional consular resources to Cairo to provide support to any British nationals affected by the demonstrations as soon as possible."
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Protesters in Egypt have been emboldened by the success of the recent uprising in Tunisia which saw President Zine al-Abidine Ben Ali ejected after 23 years in power. The pace of events has shocked observers, and led to speculation that other countries such as Yemen could be next to experience popular unrest.
