A crackdown on online games in Vietnam has seen several games' operators ordered to switch off their servers over the past month.

In the latest official move, six operators in Ho Chi Minh City, also known as Saigon, were fined, restricted or closed by the authorities.

Altogether 13 separate online games from the six companies will be shut down by the end of the year, according to local press reports.

At least one was told to turn off its servers today. Another has been ordered to immediately restrict playing time to five hours per day for each player.

"It is very difficult for us to limit the playing hours for our games. We need the assistance of foreign partners," one games developer warned local media last month.

Vietnam has a population of 80 million, and around 14 million internet connections, and internet use is growing rapidly. The majority of gamers do not own a PC, but play in internet cafés.

Estimates of the number of online gamers have ballooned from 800,000 last year to two million this year.

There are at least 13 massively multiplayer online games available in the country, with the most popular, VinaGame's Swordsman Online, reported to have 250,000 players.

The current crackdown started last year with the publication of an editorial in the official communist party newspaper, Nhan Dan, calling for more control of online games.