A British aid worker and her parents have been kidnapped by gunmen near the southern Rafah crossing in Gaza, Palestinian police say.
The woman is reported to be Scot Kate Burton, 24, from a Gaza-based human rights group called Al Mezan, but her name has not been officially confirmed.
A major security operation is under way to find the British family.
The abduction of foreigners is not unusual in the area. Hostages are usually released unharmed within hours.
Last week, two foreign teachers were taken by gunmen but quickly freed unscathed.
Generally, militant groups use the hostages to press the Palestinian authorities for money, jobs or the release of prisoners.
It is not known who is behind this latest abduction, or what they may want.
The Foreign Office confirmed there had been a kidnapping but said the details remained unclear.
Frank McGinley, of the British consulate general in Jerusalem, said officials were investigating but had no further comment.
The Palestinian police commander in Rafah told the BBC that the Britons were kidnapped at about 1600 (1400 GMT).
He said the three were travelling in a car 200m away from the border crossing when they were approached by gunmen in another vehicle.
The gunmen forced them to leave their car and go with them.
But the BBC's correspondent in Jerusalem, Jo Floto, says that a local human rights group in Gaza said that one of their female volunteers from Britain had lost contact with their office this afternoon.
Nafiz al Mahdoun, from the Al Mezan Centre for Human Rights, told BBC News 24 the missing volunteer worked for the group for the past three months but had been on holiday since 22 December.
"Her parents were visiting her. She was trying to take them around to show them the area," he said.
"So (we) are now trying to make our communication with our police and all the political parties, all the concerned people, so we could release her.
"Up to now we don't have any clear information about what's going on.
"We are trying to call her on her mobile but it's closed."