(Reuters) - Sri Lankan President Gotabaya Rajapaksa fled the country on Wednesday, hours before he was due to step down, after a people's uprising over a devastating economic crisis ended his family's powerful grip on the island nation.

Prime Minister Ranil Wickremesinghe declared a state of emergency as several hundred people surrounded his office in Colombo trying to breach the compound past police in riot gear, climbing the fences. Police fired several rounds of teargas and a military helicopter circled overhead.

"The prime minister as acting president has declared a state of emergency (countrywide) and imposed a curfew in the western province," Wickremesinghe's media secretary, Dinouk Colombage, told Reuters. Western Province includes Colombo.

As news of the president's flight spread, thousands of people gathered at the main protest site in Colombo chanting "Gota thief, Gota thief", referring to him by a nickname.

The president's flight brings an end to the rule of the powerful Rajapaksa clan that has dominated politics in the South Asian country for the last two decades.

Protests against the economic crisis have simmered for months and came to a head last weekend when hundreds of thousands of people took over key government buildings in Colombo, blaming the Rajapaksas and their allies for runaway inflation, corruption and a severe lack of fuel and medicines.