The number of Americans applying for initial jobless claims (search) plunged 36,000 last week, the largest drop in more than three years, the Labor Department (search) said on Thursday, partially because of difficulties in calculating seasonal adjustments.

New claims for state unemployment insurance benefits fell to 296,000, the lowest level since early February and the largest one-week drop since 73,000 in early December 2001, the department said.

First-time claims fell more than Wall Street expectations for them to remain unchanged from the earlier reported 330,000 in the week ended April 9.

A Labor Department analyst said the calculations used to adjust for seasonal factors had difficulties in taking into account an earlier-than-usual Easter holiday, which was in late March.

The closely watched four-week moving average, viewed by economists as a more reliable gauge of labor trends because it irons out fluctuations in the volatile weekly data, fell to 330,250 last week from 338,750 in the week ended April 9.

The so-called continued claims (search) — the number of people who remain on the benefit rolls after drawing a week of benefits — fell for the second straight week, dropping 17,000 to 2.64 million in the week ended April 9, the latest week for which data are available.