Chief Minister N Kiran Kumar Reddy unfurled the national flag and took salute during the main official function organised at NTR stadium here.
Asserting that Andhra Pradesh was able to achieve substantial progress as it was a big state which had remained united, he expressed hope that the status quo would be maintained.
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The state ministers from Telangana did not attend the event.
The Collectors hoisted the national flag and presided over the official celebrations in Seemandhra districts like Srikakulam, West Godavari and Kurnool.
The united-Andhra supporters organised cultural shows and other programmes at different places to celebrate the formation of AP and to voice the 'Samaikyandhra' (united AP) demand.
Meanwhile, TRS and other Telangana supporters, who have been observing the day as "betrayal day", hoisted black flags in Hyderabad, Warangal and other places in the region. They also took out protest rallies.