Effective Thursday, the State Securities Commission will more tightly control the value that shares can lose on a single trading day on the country's two main stock exchanges.

Under the new rules, the daily trading band will be reduced to 1 percent, plus or minus, of the day's reference price, from the previous 5 percent for securities traded on the Ho Chi Minh City Stock Exchange and to 2 percent from the previous 10 percent for securities on the Hanoi Securities Trading Center, the Vietnam News reported Wednesday.

After crossing the 1,000 mark, the VN-Index has been losing momentum since the start of this year, closing at less than 500 Tuesday, as the government battles inflation in an economy that has shown impressive growth in recent years.

"We considered tightening the trading band for some time before making this decision," commission Chairman Vu Bang said, adding the market intervention would only be a temporary measure.

One analyst, however, said the steps should have been taken earlier.