BANGKOK (Reuters) - Thailand's 81-year-old king made his first public appearance on Friday after more than a month in hospital, with hundreds of well-wishers surrounding his electric wheelchair as he visited statues of his parents.

The health of King Bhumibol Adulyadej, the world's longest-reigning monarch, is a sensitive topic in financial markets because he is the sole unifying figure in a politically polarized country with a long history of coups and upheaval.

Concerns about his health sparked a steep fall in Thai stock prices and the local baht currency on October 14 and October 15. Markets rebounded a day later. Investors, however, remain on edge, in part because of concerns about succession.

Most of Thailand's 67 million people have lived under his 63-year reign. The king's son and presumed heir, 57-year-old Crown Prince Vajiralongkorn, does not yet command his father's popular support.

A focus on the issue of royal succession would add another element of uncertainty to a polarizing four-year political crisis that has already hurt foreign investment in Southeast Asia's second-biggest economy.

Looking frail in a light-blue short-sleeved shirt with a brown blanket over his lap, King Bhumibol was wheeled into a cordoned-off area of the hospital compound, at one point slowly raising his arm and maintaining his signature solemn expression.

"I'm so relieved," said Prapada Siriwattanakarn, a 52-year old grocer after seeing him at the hospital.

The king was surrounded by a medical team who helped steer his wheelchair in an appearance that lasted less than half an hour and appeared to overwhelm hundreds of supporters who bowed and pressed their hands together in a show of respect.

Strict lese majeste laws in Thailand make comment on royal matters risky. But the king's lengthy disappearance from public view had raised concern in the largely Buddhist country where many of his subjects regard him as almost divine.

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"I'm so happy that I can't stop my tears," said Pranee Sae Wong, a 62-year old woman who had visited the hospital every day for a month for a chance to see him. "He waved his hand to the crowd and everyone said 'long live the king'."

The palace had issued daily evening updates on his condition since he was admitted with lung infection, fever and loss of appetite, and put on a saline drip.

Those updates, typically brief and opaque, usually said he was "good" or "satisfactory" and on the mend. Late on Thursday, the Bureau of the Royal Household said it would end the daily updates and make a statement only if his condition changed.

In his brief appearance, the king laid a jasmine garland in front of a monument of his mother, Princess Srinagarindra, and then another at a statue of his father, Prince Mahidol of Songkhla. He also paid respects at a statue of Thai King Rama V.

Thousands of Thais have gathered each day at Siriraj Hospital where he is being treated to sign get-well books and pray for a speedy recovery.

The king is revered as the father of the nation and the longest-reigning monarch in Thai history, projecting an image of unassailable moral authority after decades of criss-crossing Thailand helping the rural poor.

(Reporting by Jason Szep; Editing by Nick Macfie)