* Nikkei poised for biggest weekly gain since mid-April

* Some blue-chips still trading below book value

By Ayai Tomisawa

TOKYO, July 1 (Reuters) - Japan's Nikkei share average rose on Friday for a fifth day as bargain hunting continued and risk appetites remained solid after U.S. and European shares gained.

The Nikkei gained 0.8 percent to 15,701.61 in midmorning trade.

Japanese stocks have erased about the half of their losses in the wake of Britain's shock vote a week ago to leave the European Union.

For the week, the Nikkei has jumped 4.9 percent, the biggest weekly gain since mid-April.

"Excessive fears for the global economy have receded," said Takuya Takahashi, a strategist at Daiwa Securities, adding that he does not see Britain's vote to leave the European Union as leading to a global financial crisis.

Shares of securities firm gained ground, with Nomura Holdings rising 2.8 percent and Daiwa Securities advancing 1.2 percent.

Exporters were steady, with Toyota Motor Corp gaining 1.4 percent and Nissan Motor Co adding 1.1 percent.

The tumble after the Brexit vote a week ago put bellwether stocks such as Toyota and Mitsubishi UFJ Financial Group below their book values, and some of them remain there. well.

"Once investors' risk-averse stance recedes (completely), these blue-chip exporters' cheap valuations and high dividend yields will likely be reviewed by investors," Mutsumi Kagawa, senior global strategist at Rakuten Securities, wrote in a report published on Friday.

Oil refiner Idemitsu Kosan underperformed, tumbling more than 5 percent after SMBC Nikko Securities cut its rating to 'neutral' from 'outperform' in the wake of the latest news that its founding family is opposed to the planned merger with Showa Shell Sekiyu.

The broader Topix gained 0.8 percent to 1,255.83 and the JPX-Nikkei Index 400 advanced 0.8 percent to 11,335.13.

(Editing by Richard Borsuk)