At 6:30 a.m., when the morning mist disappears and the sun starts to lighten up the room, Tu heads out to the balcony to exercise. He does 1,000 hip rotations in 45 minutes.

Then he goes inside to have breakfast. Despite turning 100 last March, he walks with a straight back and without a cane.

Stroking his beard, he says: "The doctor told me not to get up too early because I might catch a cold due to the cold morning weather. So now I get up a little late. To make up, I work until 11 p.m. before going to bed."

His small room on the third floor of a house in Saigon's Binh Thanh District is filled with old books neatly arranged in shelves along the walls. In the middle of the room is a desk with a computer, which he learned to use six years ago.

Gently dragging the mouse and double clicking, he opens a folder where he has saved his unfinished documents.

In it is a draft of a book on the history of Ho Chi Minh City he had written 22 years ago on an old typewriter, hoping to publish it when Saigon turned 300 years old in 1998. But due to some personal reasons, the book never got published.

He types on the keyboard, not fast, but slowly and steadily, letter by letter. After every sentence he stops and looks at the screen to check the spellings.

"I usually type a few dozen pages a day, but sometimes only a few pages since I need to search for and verify information about certain things from other books by various authors."

His book has been accepted for publication by the Ho Chi Minh City General Publishing House.

Last year he began typing out the book based on the old version, making adjustments he saw fit. The book will be titled ‘Gia Dinh - Saigon - Ho Chi Minh City turning 322.’

"I know I don't have much time left, so I have to work hard every day. The publisher plans to have the book printed at the end of next year."

Nguyen Tu Tuong Minh, deputy director of the publisher, said: "Tu is probably the oldest author working with us. He works very professionally and enthusiastically.

"Thanks to [its] accurate facts and tons of research, it is a worthy document for readers to refer to for information."

He has published 30 books, of which the most prominent is the novel "Loan 12 Su Quan" (The Anarchy of the 12 Warlords) that he wrote when he was 60 years old while working as a bicycle repairman.

"When there were no customers, I found myself sitting and looking at the street, which was a waste of time. So I decide to write something. It took me four years to finish my first book, which was published in 1990.

In September last year it was reprinted by the Ho Chi Minh City Culture-Literature and Arts Publishing House.

He stopped repairing bicycles by the time he was 65. At that time the city renamed many of its streets. Seeing there were many new street names that were unfamiliar to him and many others, he decided to write a book to acquaint people with the new names.

To write that book, for 10 years he cycled around the city, going to each street. He went to libraries to research and contacted local authorities to collect biographical information about the people for whom the streets were named.

The result was a comprehensive book that included all kinds of information including where roads began and ended and about intersections and crossroads.

In acknowledgment of his tremendous work, in 1995 authorities asked him to join the city's Street Naming Council despite his age and the fact he was just an ordinary citizen.

Now, at the age of 100, Tu has two meals a day. For breakfast, he often eats congee or potatoes.

"I eat just enough however good or bad the food is. I don't smoke or drink alcohol or coffee. When I visit the hospital for health checks, doctors and nurses are amazed to learn I was born in 1920."

Hoang Thi Lan, 68, a neighbor, says: "He is still very healthy and does not need a cane or support from his children or grandchildren to walk. He can even take the bus by himself."

At 5:30 p.m. Tu saves the draft on the computer, takes a sip of green tea and starts to exercise. But since he is afraid of walking on the road in front of his house, which is narrow and busy, he climbs up and down the staircase in his house. In 45 minutes he has climbed nearly 1,500 steps.

After having dinner and watching the news on TV, he sits in front of his computer again.

After he had cataract surgery his eyesight are pretty good. He never complains despite sitting for hours together in a chair. His memory remains sharp.

"I feel my health is still very good for me to keep working," he said. "I still have some books I have drafted and waiting to be completed."