Nikkei flat as investors lock in profits

(Updates to midmorning)

TOKYO, May 16 (Reuters) - Japan's Nikkei stock average was flat on Friday, as investors locked in profits after four straight days of gains.

The market opened sharply higher, led by exporters and financial shares, with Mizuho Financial Group (8411.T: Quote, Profile, Research) jumping after Japan's second-largest bank said it aimed to buy back up to 400 billion yen ($3.8 billion) of its own shares in the current year.

But stocks quicky pared gains, with the Nikkei dipping into negative territory.

"The market rose on momentum, but I think it's ripe for a pause," said Kenichi Hirano, operating officer at Tachibana Securities.

As of 0116 GMT, the benchmark Nikkei .N225 was down 4.02 points at 14,247.62. The broader TOPIX index was up 0.3 percent at 1,396.58.

The market failed to sustain its earlier gains despite government data showing Japan's economy grew 0.8 percent in January-March from the previous quarter, above market expectations for a 0.6 percent increase.

Softbank Corp (9984.T: Quote, Profile, Research) fell 2.4 percent to 1,928 yen, among the biggest drag on the Nikkei.

Mizuho rose 2.4 percent to 550,000 yen. The bank booked its first quarterly loss in five years on Thursday, hit by a $2.9 billion subprime meltdown at its brokerage unit, but forecast a rebound. [ID:nT237906]