Workers were evacuated from Japan''s damaged nuclear plant after grey smoke rose from one of its reactor units on Monday.

Smoke rising from the spent fuel storage pool of Unit 3 prompted the evacuation, the latest of persistent troubles in stabilizing the radiation-leaking complex.

The smoke raises concerns about the water level in the pool needed to keep the fuel from overheating and releasing even greater amounts of radiation.

However, Japan''s chief cabinet spokesman said that monitors have not noted any significant changes in the readings.

"There are all kinds of inflammable objects inside the reactor building besides the reactor itself, therefore we would like to continue that the people working in the field will find out the cause," Yukio told a news conference in Tokyo. "However, so far, there is no problem in terms of radiation levels increasing."

The problem-plagued unit alarmed plant officials over the weekend with an unexpected pressure surge in its reactor core.

Japanese officials had reported some progress over the weekend in their battle to bring the radiation-leaking Fukushima Dai-ichi plant under control after it was damaged during the massive March 11 earthquake and tsunami that devastated northeast Japan.

But the crisis was far from over, with the discovery of more radiation-tainted vegetables and tap water adding to public fears about contaminated food and drink.

Edano confirmed that radiation levels in some farm produce exceeded the government''s provisional standards.

"However these also are not levels that will immediately harm human health," he said.

Shipping of some products, including spinach and milk, has been halted after tests found iodine exceeded safety limits.

"This is only a precautionary measure because we do not want to see very high level readings from these products over a long period of time. We will continue our monitoring and the ministry of health, labour and welfare will continue to gain information but we will continue to analyse the data, and if necessary we will have further instructions to follow," said Edano.

The toll of Japan''s triple disaster came into clearer focus on Monday after police estimates showed more than 18-thousand people died in the quake and tsunami, and the World Bank said rebuilding may cost 235 (b) billion US dollars.