Maleeha Lodhi, Pakistan's high commissioner in Britain, said search and rescue efforts in remote, mountainous regions badly hit by the quake were sure to uncover more dead.
"We fear the death toll could rise even further," she said. "This is devastating. This is the worst earthquake in Pakistan's history."
The first British team arrived in Pakistan on Saturday and had already begun work on a collapsed tower block in Islamabad.
A second team, of about 70 people, touched down in the city yesterday. The team included sniffer dogs and rescue workers from aid agencies, fire brigades and government departments.
The units are equipped with relief supplies including radios, blankets, concrete cutters, shelters and tents.
Britain's Department for International Development released £100,000 in emergency aid but said more would follow and that sum did not include the financing of the search and relief units, a spokesman said.
Ms Lodhi urged Britons, particularly those of Pakistani origin, to donate to the relief effort. She said Pakistan urgently needed search and rescue teams with equipment to break through the rubble of collapsed buildings and roads. Medicines, blankets and temporary shelters were also urgently required.
"The scale of the disaster is such that a great deal of international effort would be required and would be welcome," Ms Lodhi said. "Whatever money that comes in now will be absolutely required."
Rescue units from all over the world were already flooding into the worst hit areas last night, including a United Nations team of disaster co-ordination officials who set up three emergency centres to co-ordinate relief efforts.
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