Canada, Australia and Britain have joined the U.S. in warning their citizens of a possible security threat in the Philippines.

According to the Department of Foreign Affairs and International Trade (DFAIT), the U.S. Embassy in Manila said on Friday that "a threat against American citizens in metropolitan Manila, specifically the Pasay City neighbourhood, had been detected by reliable security forces.'

The U.S. Embassy said the threat was in effect until Oct. 10.

The DFAIT says Canadians should be extremely vigilant when travelling in Manila and other parts of the Philippines.

"Bomb attacks could occur at any time in Manila and other key cities," the agency says on its site.

"Targets could include places frequented by foreigners, such as large shopping malls and convention centres. Visitors can expect to be subject to frequent security checks at public and private facilities, including shopping malls and public transportation stations."

Radio Australia reported that the Australian government also called on its citizens to be cautious in Manila amid fears they could get caught up in an attempted attack against Americans.

And the British foreign office has warned attacks could be indiscriminate and advised Britons to exercise particular caution and extra vigilance in places frequented by foreigners.