Worries about the economic impact of the devastating earthquake as well as the nuclear power plant crisis in Fukushima cast a cloud over the Tokyo equities market Monday. Before Friday's massive quake, the Nikkei Stock Average at the Tokyo Stock Exchange was trading around the 10,500 level. But it fell more than 6 percent to close at a four-month low of 9,620.49. The 633.94 drop is the largest since Oct. 16, 2008, when the Nikkei index tumbled by 1,089.02 following the collapse of Lehman Brothers Holdings Inc. At one point Tuesday, the index fell more than 1,000 to below 8,500.

Many factors are causing the worries. The quake has hampered economic activities in large areas of the Tohoku region. Major manufacturing firms, including Toyota Motor Corp. and Honda Motor Co., have announced temporary production stoppages after some of their facilities were damaged by the quake. The firms are also facing difficulties in procuring parts from Tohoku and other regions because of traffic disruptions.

The trouble at Tokyo Electric Power Co.'s No. 1 Fukushima nuclear power plant on the Pacific coast has given rise to power shortages, hampering industrial activities. TEPCO Monday began planning rolling electricity outages — the first in TEPCO's history. They are likely to continue for some time.