By Martyn Herman

LONDON (Reuters) - Wet weather is being blamed for Wimbledon's lowest cumulative attendance for the first week since 2007 -- with numbers of fans set to drop by around 15,000 compared with last year's opening six days.

After five rain-hit days 14,483 fewer fans had walked through the gates than in the equivalent period last year.

Before Saturday's action, when the gates were closed as fans flocked to catch a bumper program, the combined attendance stood at 195,875 compared with 210,358 last year.

Attendances were down from 2015 on four of the first five days with crowds below capacity on two consecutive days for the first time since the soggy 2004 championships.

"The weather has been the main factor," an All England Club spokesman said. "Although it is important to stress that on three of the first five days we shut the gates."

With the second round not even complete by Saturday, organizers have decided to schedule matches on middle Sunday, traditionally a rest day, for only the fourth time.

Organizers made 22,000 tickets available online and they were sold out within 90 minutes of going on sale at 1400 GMT.

"This has been a difficult decision but as with other middle Sundays I am sure there will be a great atmosphere," Richard Lewis, chief executive of the All England Club, said.

Wimbledon's daily capacity is 39,000 and on Tuesday and Wednesday the attendance figure was less than that, meaning some people with tickets did not show up.

More than 39,000 attended on each of the other three days -- courtesy of Wimbledon's ticket resale policy which allows fans to buy tickets from those leaving early.

Organizers offered full or partial refunds for some ticket holders on Wednesday after less than two hours play was possible.

At least two hours' play was lost on three of the opening five days and showers continued to disrupt matches on Saturday.

(Reporting by Martyn Herman, editing by Ed Osmond and Neville Dalton)