Four anti-government protesters have been injured in an explosion outside Bangkok's international airport as demonstrators occupied its main terminal, seeking to topple the government for the second time since a 2006 coup. Cathay Pacific Airways Ltd., Singapore Airlines Ltd. and at least three other carriers canceled Bangkok flights after protesters seized the terminal last night. Tens of thousands of tourists are stranded, according to Porntip Hirunkate, secretary-general of the Tourism Council of Thailand. "We are focusing upon how we can help the tourists who want to go home," said Tharit Charungvat, spokesman for Thailand's Foreign Ministry. "The police can ask for help from military personnel to reinforce officers on the ground. They are discussing the matter." The People's Alliance for Democracy, which helped trigger the coup against former prime minister Thaksin Shinawatra, wants to force the resignation of Prime Minister Somchai Wongsawat, set to return today from the Asia-Pacific Economic Cooperation forum in Peru. He has rejected the calls and Finance Minister Suchart Thadathamrongvej said today the turmoil will hurt the country's tourism, trade and investment. "Nobody seems to be coming to the government's defense," said Michael Montesano, a visiting research fellow at the Institute of Southeast Asian Studies in Singapore. The disorder may lessen support for the protesters and make it easier for the army and police to deploy, he said. Today's blast injured four PAD supporters on an access road leading to Suvarnabhumi International Airport at around 6 a.m. this morning, Somchai Sopacharoen, the police chief in the district where the airport is located said by telephone. Police have avoided using force since an Oct. 7 clash in which two people died and 470 were injured. The SET Index of stocks dropped 1.7 percent. The measure, which has sunk 56 percent since the protests first erupted in May, is on course for its worst annual performance since the 1997 Asian financial crisis. The baht slid 0.4 percent to its lowest against the dollar in 21 months. Army Chief Anupong Paojinda met other military chiefs to discuss the protests yesterday and reiterated their commitment not to stage another coup, according to army spokeswoman Sirichan Ngathong. The Bangkok-based PAD, which includes many middle-class Thais and receives support from the country's royalist elite, accuses Somchai's ruling party of buying votes to win elections and of trying to protect Thaksin, who fled the country to escape corruption charges. Thousands of PAD activists, who have occupied Somchai's official Government House compound in central Bangkok for three months, yesterday stormed his temporary office after forcing parliament to abandon its sessions a day earlier. That postponement may affect Thailand's ability to sign international trade agreements at a summit of the Association of South East Asian Nations it is hosting Dec. 15-18. South Korea's Foreign Ministry said it was monitoring the situation and may issue a travel warning. Countries including Singapore and South Korea in September warned travelers about visiting Thailand after protesters forced the closure of its second-busiest airport in the resort of Phuket. At least five people have died since August as a result of the protests. Two people were hurt yesterday when shots were fired during a clash between protesters and pro-government supporters on a Bangkok highway, Agence France-Presse reported, citing police. Southeast Asia's fourth-busiest airport, which last year processed more than 41 million passengers, has been closed to all inbound and outbound flights since 4 a.m. this morning, Serirat Prasutanond, general manager at Suvarnabhumi Airport said in a statement posted on the airport's web site today. The airport won't reopen "until the situation returns to normal." Traffic was brought to a standstill on the six-lane road leading to the airport. Cars turned round to drive back with their hazard lights on. "I'm very angry," said Aly Mdouj, 36, a South African businessman, as he lay on his luggage inside the main terminal. "This is unbelievable. I need to get home."