The government said that a bomb scare did not mean unrest in insurgency-wracked southern Thailand had spilled over the border.

Deputy Prime Minister Najib Razak said the scare in Penang on Wednesday had only been a hoax.

"Until now, the problem in southern Thailand is restricted to the region ... it has not extended into our country," Najib was quoted as saying by the state Bernama news agency.

Thousands of commuters were enveloped in a massive traffic jam Wednesday for more than two hours after police closed a major bridge linking the holiday island of Penang to mainland Penang state to investigate the threat.

Police only found a 15-centimetre metal pipe on the bridge, according to Bernama .

"Bomb hoax phone calls that happen from time to time in this country have nothing to do with the situation in southern Thailand," said Najib, also defence minister.

Northern Malaysia and southern Thailand share a common border, while residents on both sides have close cultural and social links.

The two countries in February agreed to boost cooperation to end three years of separatist unrest in the Thailand's south in which 2,000 people have died.