Tight supply due to soaring export demand has put a lid on rice trade in Vietnam, the world's second largest exporter of the grain, dealers said on Wednesday.
Aggressive buying by China and surging demand from other importers since early March had drained supply.
China had stepped up its buying since last month, when dwindling Chinese stocks pushed prices up sharply.
"There is no rice to sell to new customers," said a trader from state-run rice trading firm Vinafood 1, adding all state-run rice businesses had been ordered by Hanoi to cease offering new deals to foreign buyers.
The trader doubted Vietnam would be able to deliver the 100,000 additional tonnes the Philippines had asked it to sell.
The National Food Authority of the Philippines asked for the extra grain after it bought 410,000 tonnes from Vietnam via a tender last month.
On Wednesday, a Vietnamese rice industry official said it was up to Hanoi to sign off on the deal.
"At the company level one cannot decide. The (Vietnam) Food Association will soon report the order to the government for permission," Truong Thanh Phong, chairman of the association, told Reuters. He gave no timeframe for a final decision.
Prices of five percent broken rice were quoted for reference only at $218 a tonne, FOB Saigon Port, unchanged from a week ago.
Prices of 25 percent broken grain also stayed static at $200-$203 a tonne.
On Tuesday, 17 vessels at Saigon Port were loading 244,756 tonnes of rice for Africa, Cuba, Iraq, Malaysia, Russia and the Philippines. Four vessels completed loading 71,457 tonnes bound for Africa, Iraq and Russia.
Traders said rice loading has been sluggish and in some cases could take up to a month, compared with the usual one week, due to the shortage of grain.