MOSCOW — After 30 years in power, the aging president of Kazakhstan jolted the oil-rich former Soviet republic and the region at large on Tuesday with the surprise announcement that he was resigning.

Nursultan Nazarbayev, 78, the last surviving president in Central Asia to have steered his country to independence after the Soviet Union collapsed, stepped away from running daily affairs, but maintained considerable authority over the sprawling country sandwiched between Russia and China.

While Kazakhs welcomed the announcement as the potential start of a new era, analysts surmised that the Kremlin would see it in a negative light by drawing attention to the nearly 20-year-old leadership of President Vladimir V. Putin and his lack of a clear succession plan.

Mr. Nazarbayev called the decision to resign difficult.

“As the founder of the independent Kazakh state, I see my task now in facilitating the rise of a new generation of leaders who will continue the reforms that are underway in the country,” Mr. Nazarbayev said in a nationally televised speech that soon led the news in neighboring Russia as well. “Until my dying day, I will stay with you. The concerns of the people will stay my concerns.”