Following are main developments after a massive earthquake and tsunami devastated northeast Japan and crippled a nuclear power station, raising the risk of uncontrolled radiation.

• Japanese military helicopters spray water on the Fukushima Daiichi nuclear reactors to try and cool fuel rods after a failed attempt the previous day because of high radiation levels. Engineers also trying to restore power to the water cooling systems.

• Plant operator says getting water to No.3 reactor priority because of smoke/steam escaping, indicating water evaporating from the cooling pool. Pressure rising in the reactor.

• The head of the U.N. nuclear watchdog says core damage at reactors 1, 2 and 3 of the plant is confirmed, but reactor vessels seem intact. Says the situation is "very serious."

• Top U.S. nuclear regulator says no water left in No. 4 reactor cooling pool, radiation levels extremely high. Latest images from the plant show severe damage to some of the buildings after several blasts.

• United States charters aircraft to fly out nationals from Japan, authorizes voluntary departure of family members of diplomatic staff.

• Kan briefs Obama on efforts to contain nuclear emergency. U.S. to fly a high-altitude drone over the stricken complex to assess the situation.

• Japan nuclear agency says radioactivity levels continue to fall at the plant. Eight staff members taking readings in shifts.

• Yen jumps 4% against the dollar, Japan's Nikkei down 2.1%. Officials blames yen spike on speculators. Bank of Japan offers to inject a further 6 trillion yen ($74 billion) into the banking system.

• Estimates of losses to Japanese output from damage to buildings, production and consumer activity range from between 10 and 16 trillion yen ($125-$200 billion), up to one-and-a-half times the economic losses from the devastating 1995 Kobe earthquake.

• G7 finance ministers will hold a conference call later on Thursday to discuss steps to help Japan cope with the financial and economic impact of the disaster.

• Australia again urges citizens in Tokyo and eight affected prefectures to consider pulling out of the country. But it said the warning was because of infrastructural problems, not the fear of radiation.

• Tokyo is safe for international travelers, the Japanese Red Cross says.

• Nuclear crisis diverts attention from the tens of thousands affected by Friday's earthquake and tsunami. About 850,000 households in the north without electricity in near-freezing weather. Death toll is expected to exceed 10,000.