Hundreds of furious Pakistanis blocked off the capital’s airport highway on Monday, demonstrating against debilitating gas shortages and pelting police with stones, witnesses said.A second angry crowd torched tyres in Islamabad and twin city Rawalpindi, throwing stones at police and private vehicles over gas rationing that has left thousands of homes without heat for hours at a time, an AFP reporter said.Frustrated with the low pressure of gas in their houses, people living in Islamabad and Rawalpindi have been turning to alternative fuels only to face the same problems, short supply and rising prices.Housewives, bakers and sweet makers in the city are willing to return to old smoky stoves but find kerosene costly and firewood hard to get.Yawning energy shortfalls frequently trigger violent protests across Pakistan, where opposition parties are setting in motion campaigns designed to force elections earlier than scheduled in February 2013.A mob blocked the main airport highway, forcing airline passengers to get out of their cars and walk with their luggage, and others to abandon their vehicles and walk home. Thick black smoke spewed into the air from burning tyres, while protesters used stones and tree branches to shut down the road, the reporter said.A police official said protesters chanted slogans against the government and demanded an end to the gas shortages.“The protesters are still on the road, even after police tried to disperse them. They are protesting against gas shortages for up to two kilometres,” said Ghulab Khan, an official in the police control room. Separately traffic in Faizabad square, which links Islamabad to Rawalpindi, was blocked for more than five hours by several hundred protesters armed with sticks.For the first time in 20 years, Rana Mohammed is using firewood to prepare sweets, samosas and other sweetmeat in his shop in Rawalpindi. Unlike the bakers who have shifted their operations to nighttime when the gas pressure becomes normal, the traditional “halwais” have to make fresh products. However, the most troubling aspect of the situation is the cost of using firewood, as its prices are rapidly rising.